glsl: relax rule on varying matching for shaders older than 4.20

glsl: relax rule on varying matching for shaders older than 4.20

This expands on commit c54c42321ea5. See the code comment for full
justifications. At the time of the previous commit Ian wanted to
limit the relaxing of the rule to GLSL 3.30 as that was the highest
version of shaders seen in the wild that were having trouble with
the stricter rules.

However since then I've found that the long standing issue with tess
shaders failing to compile in the game 'Layers Of Fear' is due to
this same issue. The game uses 4.10 shaders and also makes use of
explicit varying locations, so here we relax the rule to 4.20 and
make sure to apply the restriction to shaders using varyings with
explicit locations also.

Fixes: c54c42321ea5 ("glsl: relax rule on varying matching for shaders older than 4.00")

Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11873>