Prior to this change, uc16 was typedef'd to (unsigned) uint16_t while
uc32 was typedef'd to (signed) int32_t.

For consistency, and to avoid unexpected behavior around
signed/unsigned comparisons, this changes uc32 to the unsigned
uint32_t type.

As part of this change, old-style error passing (return -1, check for
negative return values) was updated to use named error values.

Bug: v8:10568
Change-Id: I8524e66ee20e8738749cd34c4fe82c14e885dcb3
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2235533Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Jakob Gruber <jgruber@chromium.org>
Cr-Commit-Position: refs/heads/master@{#68282}