Overhaul the Keyboard API

Overhaul the keyboard API in winit to mimic the W3C specification
to achieve better crossplatform parity. The `KeyboardInput` event
is now uses `KeyEvent` which consists of:

  - `physical_key` - a cross platform way to refer to scancodes;
  - `logical_key`  - keysym value, which shows your key respecting the
                     layout;
  - `text`         - the text produced by this keypress;
  - `location`     - the location of the key on the keyboard;
  - `repeat`       - whether the key was produced by the repeat.

And also a `platform_specific` field which encapsulates extra
information on desktop platforms, like key without modifiers
and text with all modifiers.

The `Modifiers` were also slightly reworked as in, the information
whether the left or right modifier is pressed is now also exposed
on platforms where it could be queried reliably. The support was
also added for the web and orbital platforms finishing the API
change.

This change made the `OptionAsAlt` API on macOS redundant thus it
was removed all together.

Co-authored-by: Artúr Kovács <kovacs.artur.barnabas@gmail.com>
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>
Co-authored-by: daxpedda <daxpedda@gmail.com>
Fixes: #2631.
Fixes: #2055.
Fixes: #2032.
Fixes: #1904.
Fixes: #1810.
Fixes: #1700.
Fixes: #1443.
Fixes: #1343.
Fixes: #1208.
Fixes: #1151.
Fixes: #812.
Fixes: #600.
Fixes: #361.
Fixes: #343.

.github/workflows/ci.yml

@@ -75,7 +75,6 @@ jobs:
     env:
       RUST_BACKTRACE: 1
       CARGO_INCREMENTAL: 0
-      PKG_CONFIG_ALLOW_CROSS: 1
       RUSTFLAGS: "-C debuginfo=0 --deny warnings"
       OPTIONS: ${{ matrix.platform.options }}
       FEATURES: ${{ format(',{0}', matrix.platform.features ) }}
@@ -98,12 +97,9 @@ jobs:
         targets: ${{ matrix.platform.target }}
         components: clippy
 
-    - name: Install Linux dependencies
-      if: (matrix.platform.os == 'ubuntu-latest')
-      run: sudo apt-get update && sudo apt-get install pkg-config libxkbcommon-dev
     - name: Install GCC Multilib
       if: (matrix.platform.os == 'ubuntu-latest') && contains(matrix.platform.target, 'i686')
-      run: sudo dpkg --add-architecture i386 && sudo apt-get update && sudo apt-get install g++-multilib gcc-multilib libxkbcommon-dev:i386
+      run: sudo apt-get update && sudo apt-get install gcc-multilib
     - name: Install cargo-apk
       if: contains(matrix.platform.target, 'android')
       run: cargo install cargo-apk