Implement frexp, ldexp, packUnorm2x16, unpackUnorm2x16, packUnorm4x8, packSnorm4x8, unpackUnorm4x8, unpackSnorm4x8, and unpackDouble2x32().

git-svn-id: https://cvs.khronos.org/svn/repos/ogl/trunk/ecosystem/public/sdk/tools/glslang@27738 e7fa87d3-cd2b-0410-9028-fcbf551c1848