[roll] Roll fuchsia [display][banjo][fidl] Use math.SizeU in ImageMetadata.

The SizeU instance is stored in a "dimensions" field rather than a
"size" field, because size is ambiguous (bytes vs pixels).

This CL adds a fuchsia.math/SizeU clone in the Banjo API, and adds
api-types-cpp support for converting between Dimensions and the
Banjo-generated type.

Original-Bug: 316631158
Test: fx test //src/graphics/display
Original-Reviewed-on: https://fuchsia-review.googlesource.com/c/fuchsia/+/1172175
Original-Revision: 5afe4a4d36ba13bef94f82a4909bec32ceb4949c
GitOrigin-RevId: 7265d45ab64029e57e1de482870641fdf01b6bfd
Change-Id: I8cd1325ef1b941b0a6495a6c912a0c8079f9c799

Author: Victor Costan

stem

@@ -11,7 +11,7 @@
              githooks="integration/git-hooks"
              remote="https://fuchsia.googlesource.com/fuchsia"
              gerrithost="https://fuchsia-review.googlesource.com"
-             revision="e5ac786cae4b0591c28a51b6f4cad25d4d6bdef0"/>
+             revision="5afe4a4d36ba13bef94f82a4909bec32ceb4949c"/>
   </projects>
   <hooks>
     <hook name="install-environment"