to_foo() -> to_Foo()

This tweak makes these conversion functions' names
match the names of the types, e.g. to_F32() makes F32.

Change-Id: I4d71c9bd17d835d09375e3343ee4316082b02889
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/319763
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
4 files changed