- Point size limits were left at [0,0], forcing all points to zero coverage.
  Introduce a config value for the maximum, and plumb this through to drive
  physical device limits query.

- Fix all interpolants being replaced with pointcoord

Bug: b/124177079

Change-Id: I281dd3214537f15858afbd3890cf70f8850fa4aa
Reviewed-on: https://swiftshader-review.googlesource.com/c/25489Tested-by: Chris Forbes <chrisforbes@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>