externals: Update glad to 0.1.26

loader: Fix scope error in DeconstructedRomDirectory

Updates the library from 0.1.25. Mainly fixes issues related to macOS,
but we may as well update the library.

loader: Make AppLoader_NCA rely on directory loading code

 game_list: Use QString::fromStdString() where applicable instead of c_str()

* GDBStub works with both Unicorn and Dynarmic now

* Tidy up

game_list: Join declarations and assignments in onTextChanged()

qt/main: Collapse if statement in UpdateRecentFiles()

qt: Don't show error dialog when canceling the Load Folder dialog

qt: Minor cleanup-related changes

kernel/event: Make data members private

gl_rasterizer_cache: Avoid superfluous surface copies.

 core_timing: Make GetGlobalTimeUs() return std::chrono::microseconds

qt/main: Better file-existence checking within OnMenuRecentFile() and UpdateUITheme()

This was intermixing signed and unsigned values when they could all just
be signed.

We can just use the file interfaces that Qt provides to prevent needing
to convert to std::string.

The codec used by Qt for const char* and std::string don't necessarily
have to be the same depending on locale. Therefore, we should be using
the correct functions to do the conversions.

There's no need to keep these separate from one another.

Given the function accepts a boolean, we don't need to use an if
statement here and repeat ourselves.

In OnMenuRecentFile() we don't need to construct a QFileInfo instance
just to check if a file exists, we can just use the static member
function to do that (which Qt's documentation also notes as quicker than
constructing an instance).

In UpdateUITheme(), we just want to try and open the file and check the
success of that operation. Technically speaking, between the existence
check and the open call, the file can be deleted or moved, but still
appear to succeed in code. i.e.

1. Existence check -> Returns true
2. File is moved/deleted
3. Open is called, the return value of which isn't checked
4. Nonsense behavior

This way we combine the existence check and the open into one.

Previously, when canceling out of the Load Folder dialog, a user would
get an error dialog about the selected folder not containing a main
file, however, by canceling out of the dialog, no selection was actually
made.

These occur automatically without the need to call them. While we're at
it, also std::move the QString instance into its member variable.

Makes code consistent with our style of defaulting special member
functions where applicable.

Instead we can simply provide accessors to the required data instead of
giving external read/write access to the variables directly.

memory: Correct prototype of ZeroBlock

Service/Audio: audout_a.cpp: remove pragma once

core_timing: Use transparent functors where applicable

gdbstub: Minor changes

address_arbiter: Return by value from GetThreadsWaitingOnAddress()

Implement audren audio output

ms is shorthand for milliseconds, not microseconds, and given there's no
comment indicating that this was intentional, it probably wasn't.

Enforces the time unit being returned and also allows using the standard
time utilities to manipulate it.

Keeps the code consistent.

Previously, the prototype wasn't matching the definition, which has a
Processor parameter before the destination address.

These aren't necessary, as value-wise const only matters in the
definition.