Expose box size, box color, and font override message parameters to game_text

[vrad-exe]

What would this enhancement be for?

Audio

Describe your enhancement suggestion in more detail

HUD messages defined in titles.txt have two additional parameters that can't be used with game_text - boxcolor and boxsize, which allow adding a background to the text and are most notably used for the HL2 "Saved" message. Considering that the text is rendered additive, this is a very useful feature to have to ensure messages are visible against any background and it would be nice to have these exposed as keyvalues on game_text so that the non-addon-compatible and somewhat legacy titles.txt system doesn't have to be used.

Additionally, the HUD message code supports the ability to override the scheme font per-message, but this option isn't fully exposed to users anywhere - Portal 2 does use it to select smaller/larger variants of Univers when specific message channels are used, but there is currently nowhere that allows inputting a scheme font name directly. This should also be exposed as a game_text keyvalue, and optionally also for titles.txt, but I personally wouldn't bother with the latter. For P2CE also double check that it takes priority over the channel 2/3 chapter title fonts if specified.