Migration to FPR5

[OlgaTPark]

Additional patches from Firefox ESR52 for FPR5 on Intel

This bug documents things took from https://github.com/classilla/tenfourfox/issues/457.

Not taking:

• [ ] M1402372 → Direct3D only;
• [ ] M1414945 → Not in code (numeric constant is used);
• [ ] M1423086 → Not in code;
• [ ] M1385667 → Linux-only;
• [ ] M1412420 → We support x64 but classilla says it has a performance impact, I didn't trigger it and it's maybe Windows-specific;
• [ ] M1331209 → We have asm.js but this bug is catalyzed by e10s, I didn't trigger it. Easy to fix if ever present;

Taking:

• [x] M1224396 → TenSixFox uses Skia and testcase triggers on x86 TenSixFox;
• [x] M1418447 → Same issue as the previous one. The patch replace a crash with crash-assertions;
• [x] M1415582 → In code (we use WebRTC and plugins);
• [x] M1417797 → Affects the same classes as the previous one;
• [x] M1382358 → WebGL is re-enabled and since we support old hardware, it's possible that we get spurious GLSL versions;

Others:

Note for those who will be ever interested in what I do:
Because my fork is kinda old and I need to keep up, I won't be releasing a binary version of Ten*Fox FPR5 and FPR6 Intel. Don't worry, that's not meaning I'm giving up on this!