This change was causing some issues:

> Made FMT_STRING a no-op when FMT_USE_CONSTEVAL is enabled, since the consteval format-string constructor already provides compile-time validation (#4611, #4612). Thanks @friedkeenan.

When we added the RetroAchievements integration, we had a discussion
about whether sending version information in the user agent was fine
from a privacy standpoint. We reached the conclusion that it was okay,
but it was conditional on the website having a privacy policy. Neither
incarnation of Redump has that, and Redump also never asked us to send
version information like RetroAchievements did, so let's use a user
agent that just says "Dolphin" when connecting to Redump.

When calling `ShowMessageAlert` with a given `MsgType`, log the alert
with a `LogLevel` matching the `MsgType` instead of always using
`LogLevel::LERROR`.

Remove the [[maybe_unused]] annotation from various parameters that are
unconditionally unused and comment out their names instead. This makes
it unambiguous that the variables are unused, while making the remaining
[[maybe_unused]] annotations more reliable indicators that those
variables are in fact used in some contexts.

These parameters are mostly in overridden functions where the override
doesn't need that particular variable.

Source/Core: Replace `find(x) != npos` with `contains(x)`

StringUtil: Make UTF16ToUTF8 and UTF8ToUTF16 use custom encoding/decoding implementation.

EGL is the de-facto GL context initialization API, including on X11
where it provides many additional features over GLX.

I’m planning on adding support for selecting the GPU (adapter in
Dolphin-speak) also to OpenGL, similarly to the Vulkan backend, and that
will require EGL, so let’s remove the legacy API first.

Improve usage of std::move and const references parameters