[qtbase] Add support for building with OpenGL ES 3.0

[fwcd]

This adds support for building Qt with OpenGL ES 3.0, a necessity to build many OpenGL apps for iOS.

Implementation note

The implementation follows the way the GL ES features are structured in the configure script, namely by implying gles2 and enabling gles3 only via a feature flag:

• https://github.com/qt/qtbase/blob/1ea51e1f2dfedbea306a16b2a2996ed13c29f7fd/config_help.txt#L262-L265
• https://github.com/qt/qtbase/blob/1ea51e1f2dfedbea306a16b2a2996ed13c29f7fd/cmake/configure-cmake-mapping.md?plain=1#L141-L142

Checklist

• Changes comply with the maintainer guide.
• SHA512s are updated for each updated download (doesn't apply).
• The "supports" clause reflects platforms that may be fixed by this new version.
• Any fixed CI baseline entries are removed from that file (doesn't apply).
• Any patches that are no longer applied are deleted from the port's directory (doesn't apply).
• The version database is fixed by rerunning ./vcpkg x-add-version --all and committing the result.
• Only one version is added to each modified port's versions file.

[jimwang118]

This feature passed with following triplets:

x64-linux

[m-kuhn]

You mention ios in the description, I had troubles building for ios with gles2 in the past (see https://codereview.qt-project.org/c/qt/qtbase/+/458413), is this issue solved?

[fwcd]

Yes, I could solve pretty much this exact issue by adding the gles3 feature.

[m-kuhn]

FTR: gles is deprecated on iOS https://developer.apple.com/library/archive/documentation/3DDrawing/Conceptual/OpenGLES_ProgrammingGuide/AdoptingOpenGLES3/AdoptingOpenGLES3.html, so it's correct to not put this into default features.

[data-queue]

Can you resolve conflicts?