Spanifiy content/browser/code_cache

This does several things. First, it fixes a UBSan failure:
https://luci-milo.appspot.com/ui/inv/build-8752216573640518833/test-results?q=GeneratedCodeCacheTest%2FGeneratedCodeCacheTest.WriteEntryWithEmptyData%2F0&sortby=&groupby=

I think the UBSan failure was triggered by https://crrev.com/c/5402504,
but the root cause is the call to memcpy in this code. Due to a C
language bug, memcpy actually cannot be used with some representations
of the empty slice. (See
https://davidben.net/2024/01/15/empty-slices.html )

Any C++ abstraction, like std::copy or std::ranges::copy avoids this.
But while I'm here, go ahead and replace all of this with the new
span-based APIs, which are bounds-checked.

Bug: 40284755, 40248746
Change-Id: I099442fdb140da9886e089b261ca87b2c80aad34
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5403174
Commit-Queue: Arthur Sonzogni <arthursonzogni@chromium.org>
Auto-Submit: David Benjamin <davidben@chromium.org>
Reviewed-by: Arthur Sonzogni <arthursonzogni@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1281089}