Templating here was causing a lot of redundant functions to be
generated. We can use a bit of macro magic instead of template
magic to reduce the binary size.

This reduces the size of the compile file by about 25k.

Note that the ASSIGN macro doesn't itself reduce size, but it
does save a bit of code size and makes the file look consistent.

BUG=angleproject:2022

Change-Id: I3d9a6e1739dcab1fceca3c63d2a4e35c1e847289
Reviewed-on: https://chromium-review.googlesource.com/493891Reviewed-by: Geoff Lang <geofflang@chromium.org>
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Jamie Madill <jmadill@chromium.org>