Change Marker IDs to be strings

They are hashed to uint32_t at the API boundary (SkCanvas, SkVertices),
but making them functionally strings will make the SkSL interaction much
nicer.

Change-Id: I0979871bf3d21373812129eb7e994987b3030e00
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285664
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
17 files changed