Some reorganization to avoid code duplication plus making the log screen capable of using the generic font. This also means that the popup for the log in Strife's status bar will be disabled when in generic mode - this popup with its special font would be a bit problematic.
Now, all menus will use the same scale, i.e. it only depends on the screen width and a base size of 640. This nearly universally yields better results than trying to make a 320x200 screen fit.
The only exceptions to this are the intermission screens and the level summary. These, unlike the menu need to try to make a 320x200 screen fit, but without all the hackery that was present to adjust the menu display.
Note that since this affects globally visible script variables, both the intermission and summary drawers will not use their own set but instead temporarily override the global setting as long as they run their own code.
Changing the use of variables here might cause much worse problems with menu code so it wasn't attempted
Parts of this menu suffered badly from lack of screen space to convey the intended information due to the oversized fonts. With the new font this is a lot less problematic (unless using 320x200, of course)
* re-added screen blends for images from the hardware renderer.
* moved all postprocessing of the image out of the renderers.
* cleaned out a large piece of cruft for handling the palette in the frame buffer class. This was all a remnant of the old paletted backend that no longer exists. Nowadays the screen blend is just a postprocessing effect drawn over the 3D screen, there is no need to maintain any of it as global state anymore.
* since the engine doesn't produce paletted screenshots anymore there is no need to have handling for it in the generation code. This depended on otherwise obsolete information so it got removed along with that information.
This was already far too generous and caused space problems, but with localization these became a lot worse, so now it will try to allocate at least 640 virtual pixels for the menu width and only go below that for small resolution ranges where the smaller value would result in too small text.
currentUILevel is now primaryLevel.
For ZScript, currentVMLevel was added. This is also exported as 'level' and will change as needed.
This also means that no breaking deprecations will be needed in the future, because in order to sandbox a level only 4 variables need to be handled: level, players, playeringame and consoleplayer.
The remaining global variables are not relevant for the level state.
The static 'level' has been mostly removed from the code except some places that still need work.
Most importantly, the separate command line options for switching on the legacy buffer handling have been removed.
There's really no need for them anymore, because unlike in earlier versions many of the implementation differences no longer exist - with the exception of where the light and vertex buffer contents are generated.
For testing this, -glversion 3 is sufficient.
Like Linux and macOS this will only support borderless fullscreen in the active desktop resolution now, which is what modern systems need.
The list of discrete resolutions has been removed as it makes no sense anymore with a fixed video mode - all the other scaling options remain active, though.
Lots of this was still laid out for DirectDraw. This removes most of Begin2D so that it can be done more cleanlz.
Note that this commit renders weapon sprites and screen blends incorrectly. Those will be fixed in an upcoming commit.
