Implement non-XR Gamepad discovery and input (#31200)

* Create embedder event to send to constellation

* Handle gamepad message in constellation, send to script thread

* Handle GamepadEvent in script thread and dispatch event to document

* Add missing Clones, fix event

* Add gamepad task source

* Adjust GamepadIndex type, remove unused imports

* Add internal getter for gamepads list

* Update gamepad new methods

* Handle gamepad connect and disconnect events

* Proto will be none, no need for HandleObject

* Initialize buttons and axes to standard mapping

* Adjust update type index types

* Update GamepadButton update function

* Adjust Gamepad mapping comments to match spec, add update logic

* Amend comment

* Update button and axis inputs on Updated event

* Add GilRs as gamepad backend in servoshell

* Add spec links, queue gamepad updates on task source

* ./mach fmt

* Fix comment length

* Split out button init, update spec comments

* Move gamepad event handling from document to global

* Map and normalize axes/button values

* Use std::time for gamepad timestamp

* Adjust gamepad handling in event loop

* Move button press/touch check into map+normalize function

- Small change but is more in line with spec

* ./mach fmt

* Update comment spec links and warning messages

* Doc comments -> regular comments

* Add window event handlers for gamepad connect/disconnect

* Adjust gamepad disconnect behavior

* Add missing TODO's, adjust gamepad/gamepadbutton list methods and formatting

* Update button handling from gilrs, add comments

* Enable gamepad pref during WPT tests and update expectations

* Update WPT expectations in meta-legacy-layout

Cargo.lock

@@ -2005,6 +2005,40 @@ dependencies = [
  "weezl",
 ]
 
+[[package]]
+name = "gilrs"
+version = "0.10.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "d8b2e57a9cb946b5d04ae8638c5f554abb5a9f82c4c950fd5b1fee6d119592fb"
+dependencies = [
+ "fnv",
+ "gilrs-core",
+ "log",
+ "uuid",
+ "vec_map",
+]
+
+[[package]]
+name = "gilrs-core"
+version = "0.5.10"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "0af1827b7dd2f36d740ae804c1b3ea0d64c12533fb61ff91883005143a0e8c5a"
+dependencies = [
+ "core-foundation",
+ "inotify",
+ "io-kit-sys",
+ "js-sys",
+ "libc",
+ "libudev-sys",
+ "log",
+ "nix 0.27.1",
+ "uuid",
+ "vec_map",
+ "wasm-bindgen",
+ "web-sys",
+ "windows",
+]
+
 [[package]]
 name = "gimli"
 version = "0.28.1"
@@ -2807,6 +2841,26 @@ dependencies = [
  "serde",
 ]
 
+[[package]]
+name = "inotify"
+version = "0.10.2"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "fdd168d97690d0b8c412d6b6c10360277f4d7ee495c5d0d5d5fe0854923255cc"
+dependencies = [
+ "bitflags 1.3.2",
+ "inotify-sys",
+ "libc",
+]
+
+[[package]]
+name = "inotify-sys"
+version = "0.1.5"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "e05c02b5e89bff3b946cedeca278abc628fe811e604f027c45a8aa3cf793d0eb"
+dependencies = [
+ "libc",
+]
+
 [[package]]
 name = "instant"
 version = "0.1.12"
@@ -2819,6 +2873,16 @@ dependencies = [
  "web-sys",
 ]
 
+[[package]]
+name = "io-kit-sys"
+version = "0.4.0"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "4769cb30e5dcf1710fc6730d3e94f78c47723a014a567de385e113c737394640"
+dependencies = [
+ "core-foundation-sys",
+ "mach2",
+]
+
 [[package]]
 name = "io-surface"
 version = "0.15.1"
@@ -3329,6 +3393,16 @@ dependencies = [
  "webxr-api",
 ]
 
+[[package]]
+name = "libudev-sys"
+version = "0.1.4"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "3c8469b4a23b962c1396b9b451dda50ef5b283e8dd309d69033475fa9b334324"
+dependencies = [
+ "libc",
+ "pkg-config",
+]
+
 [[package]]
 name = "libz-sys"
 version = "1.1.15"
@@ -3879,6 +3953,17 @@ dependencies = [
  "pin-utils",
 ]
 
+[[package]]
+name = "nix"
+version = "0.27.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "2eb04e9c688eff1c89d72b407f168cf79bb9e867a9d3323ed6c01519eb9cc053"
+dependencies = [
+ "bitflags 2.4.2",
+ "cfg-if",
+ "libc",
+]
+
 [[package]]
 name = "nodrop"
 version = "0.1.14"
@@ -5396,6 +5481,7 @@ dependencies = [
  "egui_glow",
  "euclid",
  "getopts",
+ "gilrs",
  "gleam",
  "glow",
  "image",