tint.h selectively includes headers depending on what features are enabled. It
is based off of the original sample code, so should give users access to all of
the functionality demonstrated in there.
This is located in include/tint/, so that users can have a pretty include of
tint/tint.h.
BUG=tint:87
Change-Id: I8659c789c154349e4e8e7730dc334da4fb6eba70
Reviewed-on: https://dawn-review.googlesource.com/c/tint/+/23124
Reviewed-by: dan sinclair <dsinclair@google.com>