Linux/x11 input handling (#7811)

Implements the basics of keyboard and mouse handling.
Some keys will need special treatment, like Backspace/Delete. In this
PR, all keys are treated as append-only. Leaving this for a follow-up.

I used @gabydd 's branch as a reference (thank you!) as well as
https://github.com/xkbcommon/libxkbcommon/blob/master/doc/quick-guide.md
For future work, I'll also use
https://github.com/xkbcommon/libxkbcommon/blob/master/tools/interactive-x11.c

All commits are separately compileable and reviewable.

Release Notes:
- N/A

---------

Co-authored-by: Mikayla Maki <mikayla@zed.dev>

script/linux

@@ -12,6 +12,7 @@ if [[ -n $apt ]]; then
     libfontconfig-dev
     vulkan-validationlayers*
     libwayland-dev
+    libxkbcommon-x11-dev
   )
   $maysudo "$apt" install -y "${deps[@]}"
   exit 0
@@ -26,6 +27,7 @@ if [[ -n $dnf ]]; then
     fontconfig-devel
     vulkan-validation-layers
     wayland-devel
+    libxkbcommon-x11-devel
   )
   $maysudo "$dnf" install -y "${deps[@]}"
   exit 0
@@ -40,6 +42,7 @@ if [[ -n $pacman ]]; then
     fontconfig
     vulkan-validation-layers
     wayland
+    libxkbcommon-x11
   )
   $maysudo "$pacman" -S --needed --noconfirm "${deps[@]}"
   exit 0