Moved Array handling from convertIndexExpression into IndexExpression

This doesn't change anything for the current code path, but makes the
logic accessible to the DSL in upcoming changes.

Change-Id: I5199e4f86ef9dea51baa2658ea2e5a8cb6434e22
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/430416
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
4 files changed