Expose more WebGL extensions

[jdm]

According to https://developer.mozilla.org/en-US/docs/Web/API/EXT_color_buffer_half_float and https://developer.mozilla.org/en-US/docs/Web/API/WEBGL_color_buffer_float these are implicitly exposed by the corresponding OES texture extensions. The tests were testing for the presence of the extension along with the ability to make use of its features.

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• ./mach build -d does not report any errors
• ./mach test-tidy does not report any errors
• There are tests for these changes

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This change is 

[highfive]

Heads up! This PR modifies the following files:

• @asajeffrey: components/script/dom/webidls/EXTColorBufferHalfFloat.webidl, components/script/dom/webgl_extensions/extensions.rs, components/script/dom/webgl_extensions/ext/mod.rs, components/script/dom/webidls/WEBGLColorBufferFloat.webidl, components/script/dom/webgl_extensions/ext/webglcolorbufferfloat.rs and 1 more
• @jgraham: tests/wpt/webgl/meta/conformance/extensions/oes-texture-float.html.ini, tests/wpt/webgl/meta/conformance/extensions/oes-texture-half-float.html.ini
• @KiChjang: components/script/dom/webidls/EXTColorBufferHalfFloat.webidl, components/script/dom/webgl_extensions/extensions.rs, components/script/dom/webgl_extensions/ext/mod.rs, components/script/dom/webidls/WEBGLColorBufferFloat.webidl, components/script/dom/webgl_extensions/ext/webglcolorbufferfloat.rs and 1 more

[jdm]

r? @nox

[nox]

This needs code changes, the 32-bit floating-point type RGBA32F becomes available as a color-renderable format only when WEBGL_color_buffer_float is enabled. There are probably similar things for EXT_color_buffer_half_float.

[nox]

I cleaned this up and will push it soon.