The logic in the code was deliberately avoiding index `2` (**Selected
Font**; the debug font) by using `std::min(index, 1)`. Presumably, the
reason was that there was no debugger in Qt version of Dolphin at the
time.

Test plan:

- Select a debug font via the **Options > Font...** action.
- Show the **Log** tab via the **View > Log** action.
- In the **Log** tab, choose the **Selected Font** item in the combobox.
- Restart Dolphin.

**Without** the patch, the **Monospaced Font** item is wrongly selected
in the combobox.

**With** the patch, the **Selected Font** item is now properly restored
from the saved settings, and the selected debug font is correctly used
in the log messages.

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...)

This fixes a memory leak that would occur when the Android frontend
calls LogManager::Init more than once in order to reload settings.

Note that the log window listener is now owned by LogManager instead of
by the frontend, making it consistent with the other log listeners.

qOverload is used to disambiguate pointers to overloaded functions, but
most of the usages in the code base were with non-overloaded functions.

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.

This should give us a nicer font on Windows, while also not severely
impacting the existing behavior on Linux.

Provides the same behvaior, but in a much more concise manner.