Add .rte -> .skvm unit test framework

Includes a handful of test cases to exercise the system

Change-Id: I98e73a8bca063f475d2ddb51778e395697392ddb
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/346637
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
diff --git a/BUILD.gn b/BUILD.gn
index 7a43e55..fc20ab0 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -783,6 +783,15 @@
     lang = "--metal"
     settings = "--settings"
   }
+  compile_sksl("skvm_tests") {
+    sources = sksl_skvm_tests_sources
+    outputPatterns = [ [
+          "/golden",
+          ".skvm",
+        ] ]
+    lang = "--skvm"
+    settings = "--settings"
+  }
   compile_sksl("spirv_tests") {
     sources = sksl_spirv_tests_sources
     outputPatterns = [ [
@@ -801,6 +810,8 @@
   }
   group("compile_sksl_metal_tests") {
   }
+  group("compile_sksl_skvm_tests") {
+  }
   group("compile_sksl_spirv_tests") {
   }
 }
@@ -813,6 +824,7 @@
     ":compile_sksl_glsl_nosettings_tests",
     ":compile_sksl_glsl_tests",
     ":compile_sksl_metal_tests",
+    ":compile_sksl_skvm_tests",
     ":compile_sksl_spirv_tests",
     ":dehydrate_sksl",
     ":run_sksllex",