Renamed SkSL "offset" to "line"

https://skia-review.googlesource.com/c/skia/+/451419 changed the meaning
of "offset" throughout SkSL, so that it was actually tracking line
numbers rather than offsets (and thus had a misleading name). This
completes the transition by renaming all of the now-misnamed "offset"
fields, parameters, and variables to "line'.

Bug: skia:12459
Change-Id: I394e6441f6ddfaad6d4098352ba9b1bfeaf273be
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/450644
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
diff --git a/src/sksl/codegen/SkSLMetalCodeGenerator.h b/src/sksl/codegen/SkSLMetalCodeGenerator.h
index e799dfb..1668e69 100644
--- a/src/sksl/codegen/SkSLMetalCodeGenerator.h
+++ b/src/sksl/codegen/SkSLMetalCodeGenerator.h
@@ -97,7 +97,7 @@
 
     void writeStructDefinitions();
 
-    void writeFields(const std::vector<Type::Field>& fields, int parentOffset,
+    void writeFields(const std::vector<Type::Field>& fields, int parentLine,
                      const InterfaceBlock* parentIntf = nullptr);
 
     int size(const Type* type, bool isPacked) const;