Make SkIPoint x() and y() constexpr

Fixes several GCC builds.

Change-Id: I9ad64b08d707a0e491590dea07617e89fe64d60d
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/246176
Commit-Queue: Brian Osman <brianosman@google.com>
Commit-Queue: Ravi Mistry <rmistry@google.com>
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Ravi Mistry <rmistry@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
1 file changed