[GLUtils] Use GL_* types for FP16 bitmap.

This patch makes sure getInternalFormat() returns GL_RGBA16F for FP16 bitmap,
getType() should return GL_HALF_FLOAT per spec
https://www.khronos.org/registry/OpenGL/extensions/OES/OES_vertex_half_float.txt,
finally, make sure checkFormat should enforce the correct format and type.

BUG: 72065799
Test: none
Change-Id: I63e79e11b1668b455e64ce20c6db806a1179fb6c