Add Enum::foreach(), change EnumValue to return SKSL_INT
Add Enum::foreach(), change EnumValue to return SKSL_INT

This gives a nicer interface (name + SKSL_INT) to getting all the values
of an enum (rather than iterating over the symbol table). Will be used
in a follow-up CL.

Change-Id: I1c104623bd06f770c57b88ca9996d3e8c87a3ca7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/379057
Commit-Queue: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Auto-Submit: Brian Osman <794c0b5534edf5601d88e1d41975d0262da12894@google.com>
Reviewed-by: John Stiles <f4fcf42d3bb5924557f1eeb3be66747535e585da@google.com>

google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,google/skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia