Correctly insert unmangled function names to symbol table This fixes detecting some cases of function parameter mismatch (previously a mangled function name corresponding to no function parameters was added to the symbol table for each user-defined function, and this was returned when doing function lookups with no parameters). Also fixes detection of reusing a function name as a variable/struct name. New unit tests are added to ensure that these fixes don't regress. BUG=angleproject:936 TEST=angle_unittests, WebGL conformance tests Change-Id: I2dadde9dcc01c7a4a653c1982c36377b89e6d437 Reviewed-on: https://chromium-review.googlesource.com/260800 Tested-by: Olli Etuaho <oetuaho@nvidia.com> Reviewed-by: Jamie Madill <jmadill@chromium.org>