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.

Qt 5.0 introduced QRegularExpression to replace QRegExp. In Qt 6.0,
QRegExp is removed entirely in favor of it.

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

DolphinQt: Replace unnecessary QStringLiterals with alternatives where applicable 

Previously, the constructor of GameConfigEdit wasn't doing anything with
the passed in parent pointer. This is dangerous because it can result in
memory being leaked in certain scenarios. It can also affect layout
decisions made by the parent. Instead, pass it through to the base class.

Current usages of the class pass in nullptr as the parent, so this is a
safe change to make with regards to the class hierarchy.

While we're at it, we can std::move the passed in QString into the class
member, allowing calling code to move strings into the constructor,
avoiding copies.

QStringLiterals generate a buffer so that during runtime there's very
little cost to constructing a QString. However, this also means that
duplicated strings cannot be optimized out into a single entry that gets
referenced everywhere, taking up space in the binary.

Rather than use QStringLiteral(""), we can just use QString{} (the
default constructor) to signify the empty string. This gets rid of an
unnecessary string buffer from being created, saving a tiny bit of
space.

While we're at it, we can just use the character overloads of particular
functions when they're available instead of using a QString overload.
The characters in this case are Latin-1 to begin with, so we can just
specify the characters as QLatin1Char instances to use those overloads.
These will automatically convert to QChar if needed, so this is safe.