AutoUpdateChecker: Fix Edge Cases

Accomplished using `run-clang-tidy` with `performance-move-const-arg,performance-unnecessary-value-param,modernize-pass-by-value`.

Changed arguments to const references, removed them where inappropriate (e.g. sink parameters). Same with std::move.

Manually reviewed each change to make sure that it makes sense, and do something more appropriate if possible.

Replace `const std::vector&` arguments with `std::span`

Don't set `s_update_triggered` if the updater process fails to be
created. This will allow users in that situation to try to start an
update later without having to restart Dolphin first.

Ignore any new update check requests if one is already in progress.

We used to create User/Logs/ as a side effect of creating
User/Logs/Mail/, but the creation of User/Logs/Mail/ was removed in
8cbfee2, so now nothing is creating User/Logs/ anymore. Let's explicitly
create it.

Set the default value of `Config::MAIN_WASAPI_DEVICE` to `default`
instead of `Default`. This fixes an issue where `AudioPane`'s `Output
Device` combo would be blank if `WASAPI` was selected and the user had
never changed the value of `Output Device`.

We don't have to worry about backward compatibility with users who have
`Default` in their config because config values aren't written unless
they've been changed at some point from the default, and the combo has
always saved `default` instead of `Default`.

Audio still worked during emulation in this situation because the
fallback for an unrecognized device name is the default device.

To help prevent similar situations in the future references to
`MAIN_WASAPI_DEVICE`'s default value now call `GetDefaultValue` instead
of hardcoding the expected default, or use the new helper function
`Config::IsDefaultValue`.