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/ir/SkSLVariableReference.cpp b/src/sksl/ir/SkSLVariableReference.cpp
index 411452c..fce77f8 100644
--- a/src/sksl/ir/SkSLVariableReference.cpp
+++ b/src/sksl/ir/SkSLVariableReference.cpp
@@ -14,8 +14,8 @@
 
 namespace SkSL {
 
-VariableReference::VariableReference(int offset, const Variable* variable, RefKind refKind)
-    : INHERITED(offset, kExpressionKind, &variable->type())
+VariableReference::VariableReference(int line, const Variable* variable, RefKind refKind)
+    : INHERITED(line, kExpressionKind, &variable->type())
     , fVariable(variable)
     , fRefKind(refKind) {
     SkASSERT(this->variable());