fix: support middle-click paste in text inputs

Paste the Linux primary selection at the clicked caret in shared input
fields, including identity import. Preserve read-only and disabled fields
and add Shift+Insert for clipboard paste. Cover mouse and keyboard paste
with GPUI interaction tests and document the supported gestures.

Co-Authored-By: GPT-6 <noreply@openai.com>

Cargo.lock

@@ -674,15 +674,30 @@ dependencies = [
  "unicode-normalization",
 ]
 
+[[package]]
+name = "bit-set"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "08807e080ed7f9d5433fa9b275196cfc35414f66a0c79d864dc51a0d825231a3"
+dependencies = [
+ "bit-vec 0.8.0",
+]
+
 [[package]]
 name = "bit-set"
 version = "0.9.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "34ddef2995421ab6a5c779542c81ee77c115206f4ad9d5a8e05f4ff49716a3dd"
 dependencies = [
- "bit-vec",
+ "bit-vec 0.9.1",
 ]
 
+[[package]]
+name = "bit-vec"
+version = "0.8.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5e764a1d40d510daf35e07be9eb06e75770908c27d411ee6c92109c9840eaaf7"
+
 [[package]]
 name = "bit-vec"
 version = "0.9.1"
@@ -1362,6 +1377,15 @@ dependencies = [
  "unicode-segmentation",
 ]
 
+[[package]]
+name = "convert_case"
+version = "0.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "affbf0190ed2caf063e3def54ff444b449371d55c58e513a95ab98eca50adb49"
+dependencies = [
+ "unicode-segmentation",
+]
+
 [[package]]
 name = "cookie"
 version = "0.18.2"
@@ -1798,7 +1822,7 @@ version = "2.1.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "799a97264921d8623a957f6c3b9011f3b5492f557bbb7a5a19b7fa6d06ba8dcb"
 dependencies = [
- "convert_case",
+ "convert_case 0.10.0",
  "proc-macro2",
  "quote",
  "rustc_version",
@@ -2758,6 +2782,7 @@ dependencies = [
  "pollster 0.4.0",
  "postage",
  "profiling",
+ "proptest",
  "rand 0.9.5",
  "raw-window-handle",
  "regex",
@@ -3775,7 +3800,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "525e9ff3e1a4be2fbea1fdf0e98686a6d98b4d8f937e1bf7402245af1909e8c3"
 dependencies = [
  "byteorder-lite",
- "quick-error",
+ "quick-error 2.0.1",
 ]
 
 [[package]]
@@ -4463,7 +4488,7 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "b2bf919621e7975acb27d881bae2fb993e0d45c8e0446e85e6272971e00dc8df"
 dependencies = [
  "arrayvec",
- "bit-set",
+ "bit-set 0.9.1",
  "bitflags 2.13.2",
  "cfg-if",
  "cfg_aliases",
@@ -5814,6 +5839,38 @@ dependencies = [
  "syn 2.0.119",
 ]
 
+[[package]]
+name = "proptest"
+version = "1.11.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4b45fcc2344c680f5025fe57779faef368840d0bd1f42f216291f0dc4ace4744"
+dependencies = [
+ "bit-set 0.8.0",
+ "bit-vec 0.8.0",
+ "bitflags 2.13.2",
+ "num-traits",
+ "proptest-macro",
+ "rand 0.9.5",
+ "rand_chacha 0.9.0",
+ "rand_xorshift",
+ "regex-syntax",
+ "rusty-fork",
+ "tempfile",
+ "unarray",
+]
+
+[[package]]
+name = "proptest-macro"
+version = "0.5.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "efaa288b896cb2b345da7b7f2110ab19e51565b83495b56fcec98a62f8b1f33e"
+dependencies = [
+ "convert_case 0.11.0",
+ "proc-macro2",
+ "quote",
+ "syn 2.0.119",
+]
+
 [[package]]
 name = "pulp"
 version = "0.22.3"
@@ -5852,6 +5909,12 @@ dependencies = [
  "bytemuck",
 ]
 
+[[package]]
+name = "quick-error"
+version = "1.2.3"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "a1d01941d82fa2ab50be1e79e6714289dd7cde78eba4c074bc5a4374f650dfe0"
+
 [[package]]
 name = "quick-error"
 version = "2.0.1"
@@ -6029,6 +6092,15 @@ dependencies = [
  "rand_core 0.10.1",
 ]
 
+[[package]]
+name = "rand_xorshift"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "513962919efc330f829edb2535844d1b912b0fbe2ca165d613e4e8788bb05a5a"
+dependencies = [
+ "rand_core 0.9.5",
+]
+
 [[package]]
 name = "range-alloc"
 version = "0.1.5"
@@ -6085,7 +6157,7 @@ dependencies = [
  "avif-serialize",
  "imgref",
  "loop9",
- "quick-error",
+ "quick-error 2.0.1",
  "rav1e",
  "rayon",
  "rgb",
@@ -6512,6 +6584,18 @@ version = "1.0.23"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "cf54715a573b99ac80df0bc206da022bcd442c974952c7b9720069370852e21f"
 
+[[package]]
+name = "rusty-fork"
+version = "0.3.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "cc6bf79ff24e648f6da1f8d1f011e9cac26491b619e6b9280f2b47f1774e6ee2"
+dependencies = [
+ "fnv",
+ "quick-error 1.2.3",
+ "tempfile",
+ "wait-timeout",
+]
+
 [[package]]
 name = "rustybuzz"
 version = "0.20.1"
@@ -7503,7 +7587,7 @@ dependencies = [
  "fax",
  "flate2",
  "half",
- "quick-error",
+ "quick-error 2.0.1",
  "weezl",
  "zune-jpeg",
 ]
@@ -7964,6 +8048,12 @@ dependencies = [
  "uuid",
 ]
 
+[[package]]
+name = "unarray"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "eaea85b334db583fe3274d12b4cd1880032beab409c0d774be044d4480ab9a94"
+
 [[package]]
 name = "unicase"
 version = "2.10.0"
@@ -8260,6 +8350,15 @@ dependencies = [
  "libc",
 ]
 
+[[package]]
+name = "wait-timeout"
+version = "0.2.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "09ac3b126d3914f9849036f826e054cbabdc8519970b8998ddaf3b5bd3c65f11"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "waker-fn"
 version = "1.2.0"
@@ -8586,8 +8685,8 @@ source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2f519832254e56965a9940c4af57dcb75f702b6f6fa4a0b172f685395843a4d7"
 dependencies = [
  "arrayvec",
- "bit-set",
- "bit-vec",
+ "bit-set 0.9.1",
+ "bit-vec 0.9.1",
  "bitflags 2.13.2",
  "bytemuck",
  "cfg_aliases",
@@ -8658,7 +8757,7 @@ dependencies = [
  "android_system_properties",
  "arrayvec",
  "ash",
- "bit-set",
+ "bit-set 0.9.1",
  "bitflags 2.13.2",
  "block2 0.6.2",
  "bytemuck",