Move symbol table initialization to SymbolTable.cpp This is needed in order to make symbol table symbols statically allocated. BUG=angleproject:2267 TEST=angle_unittests Change-Id: Ia2d44fb30d49dc5d5c67643fe01280c89127a3c3 Reviewed-on: https://chromium-review.googlesource.com/889299 Reviewed-by: Jamie Madill <jmadill@chromium.org> Reviewed-by: Corentin Wallez <cwallez@chromium.org> Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>