Move ProgramImpl definitions into Processor subclass headers.

Move ProgramImpl function definitions into Processor subclass cpp files.

Delete separate h/cpp files.

Modify GrGLSLVaryingHandler::addPassThroughAttribute to break #include
cycle. It now takes a ShaderVar rather than a GP::Attribute, making
it slightly more flexible as the input can be any variable defined
in the vertex shader.

Bug: skia:11358
Change-Id: I94ee8cd44d29e194216592ecae5fd28de785c975
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/438596
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
Commit-Queue: Brian Salomon <bsalomon@google.com>
diff --git a/src/sksl/dsl/priv/DSLWriter.h b/src/sksl/dsl/priv/DSLWriter.h
index ae79be6..56b1db3 100644
--- a/src/sksl/dsl/priv/DSLWriter.h
+++ b/src/sksl/dsl/priv/DSLWriter.h
@@ -20,7 +20,7 @@
 #include "src/sksl/ir/SkSLExpressionStatement.h"
 #include "src/sksl/ir/SkSLProgram.h"
 #if !defined(SKSL_STANDALONE) && SK_SUPPORT_GPU
-#include "src/gpu/glsl/GrGLSLFragmentProcessor.h"
+#include "src/gpu/GrFragmentProcessor.h"
 #endif // !defined(SKSL_STANDALONE) && SK_SUPPORT_GPU
 #include <list>
 #include <stack>