[clang-tools-extra] Reapply "[clang-doc] Move Info types into arenas (#190054)" (PR #192495)

[Paul Kirth via cfe-commits]

ilovepi wrote:

@dyung, I got the clang-extra tests enabled in our CI and tested this patch on it: https://ci.chromium.org/ui/p/fuchsia/builders/toolchain.ci.shadow/clang-mac-x64/b8684421852744222065/overview

The ninja command can be found in this log: https://logs.chromium.org/logs/fuchsia/buildbucket/cr-buildbucket/8684421852744222065/+/u/clang/test/l_execution_details

Should we try this on the bot before landing?

https://github.com/llvm/llvm-project/pull/192495