Continuous keyboard map scrolling

[torradmin]

Summary

Binding "Scroll East/West/North/South" to a key now scrolls the map continuously
while the key is held, matching edge scrolling and mouse-drag scrolling. Before,
each press moved the map a single fixed step, because Windows key-repeat events
never reach the game's keyboard buffer — repeating the scroll required releasing
and pressing the key again. Held keyboard scroll ramps up to the same top speed
as edge scrolling and honors the "Scroll speed" option.

Behavior classification

• Keyboard scroll: fixed — the four scroll commands are documented and bound
  by default but were effectively inert for sustained scrolling; this makes them
  work as a modder/player would expect from an edge-scroll-equivalent command.

No compatibility boundary (saves, replays, network, data formats) is touched;
this is local input handling only.

Documentation

Manual change records added:

• manual/changes/keyboard-scroll-continuous.md
• manual/changes/keyboard-scroll-diagonals-and-modifiers.md

Validation

• Verified via manual testing that keyboard scrolling now works at a similar speed to edge scrolling and respects the scroll speed selected.

[tomsons26]

Gonna block this for now as we need to look into how RA2 handles modifiers and repeats.
It probably shows a more intended way to handle this.

[ZivDero]

Gonna block this for now as we need to look into how RA2 handles modifiers and repeats. It probably shows a more intended way to handle this.

Yeah IIRC RA2 adds the key input with modifiers as Execute() argument, should look into it. This PR seems to be a bit overreaching.

[torradmin]

Gonna block this for now as we need to look into how RA2 handles modifiers and repeats. It probably shows a more intended way to handle this.

Not sure where to find the RA2 source code? I looked at OpenRA and made some fixes based on that for checking modifier keys.

[torradmin]

Gonna block this for now as we need to look into how RA2 handles modifiers and repeats. It probably shows a more intended way to handle this.

Yeah IIRC RA2 adds the key input with modifiers as Execute() argument, should look into it. This PR seems to be a bit overreaching.

Removed the ESC/ALT+TAB fixes from this to be a bit less overreaching. :)