Add anonymous members as a new symbol table type, so the infrastructure can handle blocks with no names.

Also, add more safety to the types involved regarding copy constructors, operator=, etc.

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@21106 e7fa87d3-cd2b-0410-9028-fcbf551c1848