Missing float color buffer tests

[lexaknyazev]

EXT_color_buffer_half_float

In WebGL 1.0 contexts, the 16-bit floating-point types RGB16F and RGBA16F become available as color-renderable formats. Renderbuffers can be created in these formats.

• The EXT_color_buffer_half_float tests do not check if half-float renderbuffer creation succeeds in WebGL 1.0 with the extension enabled.
• This extension is implicitly enabled by OES_texture_half_float. The tests for the latter also do not cover successful half-float renderbuffer creation.

WEBGL_color_buffer_float

The 32-bit floating-point type RGBA32F becomes available as a color-renderable format. Renderbuffers can be created in this format.

• The combined OES_texture_float/WEBGL_color_buffer_float tests do not check if float renderbuffer creation succeeds in WebGL 1.0 with either extension enabled.