Add a spacer between the alert text and Connect button to prevent the
alert text from migrating down with larger window heights.

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.

There is no longer any major reason for why this function would
need to return the same result for all players.

Instead of comparing the game ID, revision, disc number and name,
we can compare a hash of important parts of the disc including
all the aforementioned data but also additional data such as the
FST. The primary reason why I'm making this change is to let us
catch more desyncs before they happen, but this should also fix
https://bugs.dolphin-emu.org/issues/12115. As a bonus, the UI can
now distinguish the case where a client doesn't have the game at
all from the case where a client has the wrong version of the game.

Ridiculously long nicknames cause UI silliness, so 30 characters seems
like a reasonable limit, as it's the same as the forum.

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