Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

If the call to `Open` a perf map fails don't set `s_is_enabled` (though
it could already be true if you're also using VTUNE) and don't call
`std::setvbuf` with a null stream.

Also fix a typo in a comment (`if` -> `in`)

Use IOFile's bool operator to check that it's not just open but good.

Set `s_is_enabled` to `true` in `Init` when `USE_VTUNE` is defined so
that `IsEnabled` returns true even if perf isn't being used.

The check only happened if `USE_VTUNE` wasn't defined, and in that case
it was immediately followed by the same check again.

The check used to avoid an unnecessary call to `StringFromFormatV` in
certain circumstances, but that call was removed in
be81fe86e19e3afc70fc9190fd8f5f18f906c0eb.

OProfile is not used at all these days, most major distributions do not ship it anymore (Debian, Fedora, and Alpine to name the few I've checked) and following a discussion on Discord, nobody is apparently using it, most devs not even being aware of it. This removes an optional dependency from Dolphin.

Makes the namespace consistent with other common utilities.

Prefer fmt to printf-style formatting.

SPDX standardizes how source code conveys its copyright and licensing
information. See https://spdx.github.io/spdx-spec/1-rationale/ . SPDX
tags are adopted in many large projects, including things like the Linux
kernel.