Reduce the size of DSLType.

This CL removes the TypeConstant member from DSLType. The constructor
which takes a TypeConstant now sets the `fSkSLType` field immediately
instead of saving the value and deferring lookup until `skslType()` is
called.

This caused some ripple-effect issues in type setup code which were
fixable by replacing nullptr with Poison.

Change-Id: I8fa73cdf5f0bcd3de143c9a25ea43392d75c7dec
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/545780
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
3 files changed