Enable bugprone-undefined-memory-manipulation clang-tidy warning.

An initial clang-tidy pass revealed that 90% of the warnings were
triggered by WTF's container types. These warnings are (hopefully) false
positives since the use of memcpy/memmove/memset is guarded by traits
which promise that the type in question is safe to use with those
functions and have been suppressed using NOLINTNEXTLINE comments.

There are fewer than 100 failures outside of //third_party; given that
this warning seems fairly high value, enable it now rather than blocking
on addressing all existing violations first.

Bug: 1393130
Change-Id: Ie6a9b516c9b2d257a037687842e8473be9f9c443
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4056395
Reviewed-by: Jeremy Roman <jbroman@chromium.org>
Commit-Queue: Daniel Cheng <dcheng@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1075827}

.clang-tidy

@@ -8,6 +8,7 @@
                     bugprone-inaccurate-erase,
                     bugprone-string-constructor,
                     bugprone-string-integer-assignment,
+                    bugprone-undefined-memory-manipulation,
                     bugprone-unused-raii,
                     bugprone-use-after-move,
                     google-build-explicit-make-pair,