OpenGL immediate mode: drawarmature.c

Changed the color function to output a float[4] to use with shaders.
Temporary leaving the UI_ThemeColor/glColor function.
Porting draw_bone_octahedral (wire) to Batch API.

Gawain : Added Batch_init()

to init a batch without allocating memory

OpenGL immediate mode: interface_draw.c (end)

Eradicate leftover legacy functions.
Fix a crash with histogram resolution.

OpenGL immediate mode: interface_draw.c (cont)

ui_draw_but_TRACKPREVIEW

Changed stipple shader usage to a bunch of GL_LINES with flat color

OpenGL immediate mode: Added replacement for glaDrawPixelsTex_*

OpenGL immediate mode: interface_draw.c (cont)

ui_draw_but_CURVE

cleanup from recent commits

coding style, float literals

Converted some (expr / literal) to (expr * literal) where it does not impact readability.

Simplified a few function calls.

OpenGL immediate mode: clip_graph_draw.c

Part of T49043 and T49042

OpenGL immediate mode: gluSphere replacement

Updated interface_draw.c to use the new sphere batch.

OpenGL immediate mode: fix Waveform Font color

OpenGL immediate mode: interface_draw.c (cont)

ui_draw_but_UNITVEC
Introduced a new shader to be used for simple lighting.

OpenGL immediate mode: interface_draw.c (cont)

ui_draw_but_COLORBAND
Introduced a new checker shader to be used mostly on transparent areas.

OpenGL immediate mode: Convert leftover UI_ThemeColor calls

Some `UI_ThemeColor` calls were left in converted files, in some cases
because they were just overlooked, and in the case of text drawing,
because the new BLF color functions were not yet implemented at the
time of conversion.

Also converted one `drawcircball` call that was left in
transform_constraints.c

Part of T49043

fix clang warning

uninitialized variable (glGen functions set the value)

OpenGL immediate mode: uvedit_draw.c

Still has one `UI_ThemeColor` call, because drawing is happening in a DM
drawing callback which hasn't been converted yet.

Also has some old gl calls that are #ifdef'ed out.

This also changes active face drawing in UVs from stippled to a solid
color, which makes active faces much more visible, and also looks nicer.
The same should probably be done for active face drawing in the 3d view.
(has been discussed with merwin on IRC)

Part of T49043