Generalized TriangleBenchmark to support rendering a triangle of a solid
color (hard-coded in shader), interpolated input colors, and
interpolated colors with texture sampling. Added benchmark captures for
each type, along with multi-sampled versions of each.

Bug: b/176981107
Change-Id: Iadef1f0f9a339038198f8ef0e492c4c2909a96b2
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/51889Tested-by: Antonio Maiorano <amaiorano@google.com>
Commit-Queue: Antonio Maiorano <amaiorano@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Kokoro-Result: kokoro <noreply+kokoro@google.com>