tint/transform: Refactor transforms

Replace the ShouldRun() method with Apply() which will do the
transformation if it needs to be done, otherwise returns
'SkipTransform'.

This reduces a bunch of duplicated scanning between the old ShouldRun()
and Transform().

This change also adjusts code style to make the transforms more
consistent.

Change-Id: I9a6b10cb8b4ed62676b12ef30fb7764d363386c6
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/107681
Reviewed-by: James Price <jrprice@google.com>
Kokoro: Kokoro <noreply+kokoro@google.com>
Commit-Queue: Ben Clayton <bclayton@google.com>
Reviewed-by: Dan Sinclair <dsinclair@chromium.org>

src/tint/sem/variable.h

@@ -23,6 +23,7 @@
 
 #include "src/tint/ast/access.h"
 #include "src/tint/ast/address_space.h"
+#include "src/tint/ast/parameter.h"
 #include "src/tint/sem/binding_point.h"
 #include "src/tint/sem/expression.h"
 #include "src/tint/sem/parameter_usage.h"
@@ -212,6 +213,11 @@ class Parameter final : public Castable<Parameter, Variable> {
     /// Destructor
     ~Parameter() override;
 
+    /// @returns the AST declaration node
+    const ast::Parameter* Declaration() const {
+        return static_cast<const ast::Parameter*>(Variable::Declaration());
+    }
+
     /// @return the index of the parmeter in the function
     uint32_t Index() const { return index_; }