This makes the code simpler across the board. There are a few cases
where mangled names still need to be generated in AST traversers, but
they are outweighed by much leaner output code for all function nodes.

BUG=angleproject:1490
TEST=angle_unittests, angle_end2end_tests

Change-Id: Id3638e0fca6019bbbe6fc5e1b7763870591da2d8
Reviewed-on: https://chromium-review.googlesource.com/461077
Commit-Queue: Olli Etuaho <oetuaho@nvidia.com>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>