ESSL 1.00 spec allows for variable with same name to override outer variable
inside of a nested scope. This change adds new scope to symbol table inside
of a function defintion, but after function parameters for ESSL 1.00
shaders (but not webGL). This prevents an error while parsing.

This also includes some new code in translator to rename any vars that are
redefined between the function body and the function parameters. This
prevents an error later on when the translated shader is then parsed as
a desktop GLSL version.

Bug: angleproject:3287
Change-Id: I3f025805cf8d65bf912283bb15e6dad6e5e9b967
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1601553
Commit-Queue: Tobin Ehlis <tobine@google.com>
Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org>