Cleaned up DSL error handling

This unifies various chunks of error handling code and makes the DSL
more gracefully handle failed object construction.

Change-Id: I4edc581c9eba276ce2ee2a17125ea7bd6057134a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/420237
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
10 files changed