Added DSLSymbols

These are new APIs to manage symbols and symbol tables from DSL code,
needed for the upcoming DSLParser.

Change-Id: Ic8d86aebfbcdeb84bd872d8727cdfafbb8db2fd6
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/414907
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
diff --git a/gn/sksl.gni b/gn/sksl.gni
index 7cba39e..77fd4e8 100644
--- a/gn/sksl.gni
+++ b/gn/sksl.gni
@@ -29,6 +29,7 @@
   "$_include/sksl/DSLModifiers.h",
   "$_include/sksl/DSLRuntimeEffects.h",
   "$_include/sksl/DSLStatement.h",
+  "$_include/sksl/DSLSymbols.h",
   "$_include/sksl/DSLType.h",
   "$_include/sksl/DSLVar.h",
   "$_src/sksl/SkSLASTFile.h",
@@ -86,6 +87,7 @@
   "$_src/sksl/dsl/DSLLayout.cpp",
   "$_src/sksl/dsl/DSLRuntimeEffects.cpp",
   "$_src/sksl/dsl/DSLStatement.cpp",
+  "$_src/sksl/dsl/DSLSymbols.cpp",
   "$_src/sksl/dsl/DSLType.cpp",
   "$_src/sksl/dsl/DSLVar.cpp",
   "$_src/sksl/dsl/priv/DSLFPs.cpp",