Always include library_sdl.js and library_glfw.js conditionally. NFC

[sbc100]

Split out from #19028.

As of #18443, USE_SDL defaults to zero which means we don't want to include
library_sdl.js by default, even when AUTO_JS_LIBRARIES is set.

In order to make closure happy without library_sdl.js but with INCLUDE_FULL_LIBRARY
I had to add a closure type annotation for the Module.ctx object. I'm really not sure
why this was needed now but not before.

[dschuff]

I'm all for not having libraries magically included if not used; but we should probably have a changelog for this, right? Since this will break people who aren't using -lsdl or -lglfw if they should?

[sbc100]

I'm all for not having libraries magically included if not used; but we should probably have a changelog for this, right? Since this will break people who aren't using -lsdl or -lglfw if they should?

For glfw there is no change at all since USE_GLFW=2 is still the default.

For USE_SDL, we changes the default to 0 back in #18443 so users have to opt into using SDL already.

In other words I would argue this is very close to NFC.

[dschuff]

oh, they need to USE_SDL=1 to get the SDL C headers?

[sbc100]

oh, they need to USE_SDL=1 to get the SDL C headers?

Yes, as of #18443 that is needed. Users who don't specify USE_SDL will see #error "To use the emscripten port of SDL use -sUSE_SDL or -sUSE_SDL=2.

[juj]

Looks nice overall.