Trace enum values by name for mojo generated enums

Trace values of enums that are not typemapped or native-only as their
names to improve readability of traces of mojo enum parameters.

Bug: 1103623
Change-Id: I2ebd1f48fc76892f21b2386a5d61816a2394fa3a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2299722
Reviewed-by: Eric Seckler <eseckler@chromium.org>
Reviewed-by: Alexander Timin <altimin@chromium.org>
Reviewed-by: Oksana Zhuravlova <oksamyt@chromium.org>
Commit-Queue: Karel Král <karelkral@google.com>
Cr-Commit-Position: refs/heads/master@{#788991}