Per discussion in the WebGL working group, shaderSource no longer
generates INVALID_VALUE for sources containing characters outside the
ESSL character set. Compilation and/or linking is still specified to
fail when illegal constructs are used.

With this change, https://github.com/KhronosGroup/WebGL/pull/3206
passes with the passthrough command decoder.

Revise WebGL compatibility tests to follow the new rules.

Bug: chromium:1171506
Change-Id: Id132e0b64fa94b373f2732acf2a7071f38f0d4ff
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2654264Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Jonah Ryan-Davis <jonahr@google.com>
Commit-Queue: Kenneth Russell <kbr@chromium.org>