Add ability to treat keywords as identifiers in versions that had not yet reserved the keyword.

Used this for precision keywords and double matrix keywords.

Also added a few missing reserved words.

Also removed redundant "syntax error" when there is a parse error.


git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@20423 e7fa87d3-cd2b-0410-9028-fcbf551c1848