Towards a simpler SkSL -> GLSL pipeline (and better shader reflection)

The pretty printer didn't actually need the original (separate) strings,
so make it just operate on a single SkSL::String. Also remove the unused
line numbering, and the unit test. (Testing of test code, yay!)

With that done, cut down on passing around arrays of char* + length, and
just do the compaction to a single SkSL::String in the program builder.

Change-Id: Ieef9d9a8e3c5620c011b17477f1b0f9a9faa6273
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/208226
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
12 files changed