GL/GLES: implement mapping for various texture formats

[sarbes]

Description

This PR provides a mapping from Kodi textures to the respective GL/GLES formats.

Motivation and context

This PR brings us one step closer to have texture formats other than BGRA.

The PR does not introduce a check if the format is supported. A supplied texture might be uploaded to the GPU, be converted by the driver to a suitable internal format, or might fail silently (defaulting to a black texture). Such a check should be done earlier (and is not part of this PR).

How has this been tested?

Compiles and runs fine on GL/GLES. There might be bugs concerning the newly implemented (unused) formats, but they won't cause user facing issues.

What is the effect on users?

None.

Screenshots (if appropriate):

Types of change

• Bug fix (non-breaking change which fixes an issue)
• Clean up (non-breaking change which removes non-working, unmaintained functionality)
• Improvement (non-breaking change which improves existing functionality)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that will cause existing functionality to change)
• Cosmetic change (non-breaking change that doesn't touch code)
• Student submission (PR was done for educational purposes and will be treated as such)
• None of the above (please explain below)

Checklist:

• My code follows the Code Guidelines of this project
• My change requires a change to the documentation, either Doxygen or wiki
• I have updated the documentation accordingly
• I have read the Contributing document
• I have added tests to cover my change
• All new and existing tests passed

[lrusak]

I would highly recommend splitting gles stuff out of CGLTexture into CGLESTexture before implementing this PR. Even if there is code duplication it makes the abstraction easier and the code more readable without the ifdeffing.

[jenkins4kodi]

@sarbes this needs a rebase