Simplify the sampler object code path selection in GL backend

[goodartistscopy]

Sampler Objects are now used only based on the m_samplerObjectSupport boolean, in line with m_gles3 being discovered at runtime due to WebGL.
This should also fix the issue reported in an earlier PR #2947 (@PyryM)

[bkaradzic]

This change doesn't work with wasm/WebGL.

[goodartistscopy]

I specifically tested this to fix a WebGL2 problem in our app. I can confirm that sampler states are now correctly set.
After your prompt, I double checked that this did not break on WebGL1 and it doesn't. Am I missing something ?

Note that I build with BGFX_CONFIG_RENDERER_OPENGLES=30 to allow for both WebGL1 and 2 at runtime.
BGFX_CONFIG_RENDERER_OPENGLES=20 can't emit Sampler Object API, so I'm adding an additional sentinel:

m_samplerObjectSupport = false
	|| m_gles3 && BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30)
	|| s_extension[Extension::ARB_sampler_objects].m_supported
	;

With that all the configurations I tested look fine.

[bkaradzic]

Yeah it works now.

[bkaradzic]

But this is incorrect:

			m_samplerObjectSupport = false
					|| m_gles3 && BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30)

It should be just m_gles3, and something is missing about importing those sampler object functions so they turn to be null in WebGL.

Try removing && BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30), and then run example-06-bump.

[goodartistscopy]

With just m_gles3 and sampler object calls undefined it crashes. Or do you mean empty stubs ? but then they won't do what they should, instead of using the legacy API. I'm a bit puzzled.
When I missed && BX_ENABLED(BGFX_CONFIG_RENDERER_OPENGLES >= 30) on my first try, BGFX_CONFIG_RENDERER_OPENGLES=20 was indeed crashing on a webgl 2 enabled browser (peculiar configuration, but still allowed)

[bkaradzic]

Try this fix:
9e7aa2d

[goodartistscopy]

Works like a charm, I missed those "GL_IMPORT____x()". Updating to just the rest of the simplifications. Thanks.