Clean up webgl-test-utils.js

Fix behavior when automatically determining the type of a shader.
Previously the second shader in setupProgram could get assigned the type
of the first shader in case only the type of the second shader was
specified in its script tag, possibly resulting in confusing errors.

The shaderType logic in loadShaderFromScript was also needlessly
complicated, so simplify it.

In addition, fix some typos, add missing docs, and remove duplicate of
setupSimpleTextureProgram.

These fixes are meant to ease development of new tests, and aren't ported
back to earlier versions of the test suite.
Clean up fullscreen related functions in webgl-test-utils.js

Remove unnecessarily complicated findElement sub-function, make
fullscreenStateNames private to the function that uses it, put docs where
they belong and add in missing docs.

Only manual/framebuffers-keep-contents-exiting-fullscreen-mode.html is
using this functionality of the test utils, and has been tested to work
with these changes.

This change is meant to ease development of new tests, and is not ported
back to earlier versions of the test suite.
Merge pull request #382 from NVIDIA/test-utils-fixes

Test utils fixes