Add a red flash when the player takes damage.

[MeLoNaCo]

Issue #1743
I updated the player's GotHitAnimation node to flash between red, white, transparent red, and white when taking damage.

[manuq]

@MeLoNaCo as you have found, a "got hit" animation already existed, but it was more subtle (the player going from semitransparent to fully visible). Please attach before/after videos so we can see the difference. It very useful attach videos or images in these kind of tasks.

[github-actions]

Play this branch at https://play.threadbare.game/branches/MeLoNaCo/main/.

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

[manuq]

@MeLoNaCo looks great! Please update the pull request title and description to reflect the actual changes (white, not red). Also the description should have a last line saying "Resolves URL" being URL the link to the task. See https://github.com/endlessm/threadbare/wiki/Contributing#pull-request-descriptions

After you do the changes in title and description, we can merge it.