Input hints: Display logical keys

[wjt]

Our keybindings are, correctly, configured to use the physical location
of keys on the keyboard. This is because WASD are chosen to be the same
shape as the arrow keys, not because "W" means up; and so other bindings
such as Z and X must also be physical to avoid clashing.

However this means the labels are wrong for QWERTZ and AZERTY keyboards:

Action	QWERTY	QWERTZ	AZERTY
Up	W	W	Z
Left	A	A	Q
Down	S	S	S
Right	D	D	D
Throw	X	X	X
Repel	Z	Y	C

We don't actually show WASD in the UI, but we do show X for Throw and Z
for Repel.

Rather than hardcoding that the glyph for Repel is Z on a keyboard and
L1 on a gamepad, instead look these up dynamically.

Change the resources to be based on the Key / JoyButton / etc. enums.
Rewrite the importer accordingly to generate just one resource per
device type (which contains all the necessary AtlasTextures) rather than
hundreds of separate AtlasTexture resources. (It was my idea to do the
latter; I was wrong!)

Update to Kenney Input Prompts 1.5; among other things this introduces a
glyph for the "Pause" key on a keyboard, which we do actually have a
binding for. But only check in the four sheets that we actually use.

Then in the input hint controls, determine which key/button the event is
bound to, and display that.

There are some annoying edge cases to handle, including:

• R2 is analogue so is represented in Godot as an axis that can never be
  negative, but we present it as a button;
• The arrow keys want to be treated like a joystick in the UI;
• We show mouse + keyboard controls for some actions;
• Sony helpfully relabelled the Start/Select buttons from PS3 (and
  older) to something else in PS4 and something else again in PS5.

Resolves #2185

[wjt]

Needs rebase; conflicts due to #2331.

Also needs testing on the web platform.

[github-actions]

Play this branch at https://play.threadbare.game/branches/endlessm/wjt/rewrite-input-hud-again/.

(This launches the game from the start, not directly at the change(s) in this pull request.)

[wjt]

TODO: keyboard_get_keycode_from_physical is not supported on the web platform

index.js:467 ERROR: Not supported by this display server.
onPrintError @ index.js:467
index.js:467 at: keyboard_get_keycode_from_physical (servers/display/display_server.cpp:1211)

[wjt]

Physical bindings work on the web but that's because at the time the keyboard event is delivered, both the physical and logical codes are provided:

https://developer.mozilla.org/en-US/docs/Web/API/KeyboardEvent#instance_properties

There is an API to do the lookup, but only in Chromium:

https://developer.mozilla.org/en-US/docs/Web/API/Keyboard/getLayoutMap

I wonder if there is a widely used workaround.

[wjt]

But in the worst case we can just make this call conditional on "is not the web", and fall back to the current behaviour.