Convert IRGenerator::convertBinaryExpr to BinaryExpr::Make.

Interestingly, this reduces the size of our dehydated data
significantly, because we were storing the result type of the binary
expression explicitly. Now the result type is deduced automatically from
the left and right types by the Make call.

Change-Id: Ic6187a5c36774f5a4ed2ec579e9cd13b331832b5
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/377099
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
11 files changed