Migrate inliner-related tests to a separate unit-test file.

All tests are now GLSL-based instead of .fp based, for ease of
readability. DEF_TESTs which called test() more than once have been
split up into a separate individual DEF_TEST for each test() call, to
simplify fixups going forward.

Change-Id: I9202e95e9cafff3efc0c32aa3f3ca2eea04719fe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/314886
Reviewed-by: Brian Osman <[email protected]>
Commit-Queue: John Stiles <[email protected]>
Auto-Submit: John Stiles <[email protected]>

Author: johnstiles-google

gn/tests.gni

@@ -262,6 +262,7 @@ tests_sources = [
   "$_tests/SkSLErrorTest.cpp",
   "$_tests/SkSLFPTest.cpp",
   "$_tests/SkSLGLSLTest.cpp",
+  "$_tests/SkSLInlinerTest.cpp",
   "$_tests/SkSLInterpreterTest.cpp",
   "$_tests/SkSLMemoryLayoutTest.cpp",
   "$_tests/SkSLMetalTest.cpp",