Remove Startup Delay

[jwood00]

Just a suggestion based on personal preference, but I would love to see an option to disable loading the overlay's achievement images at startup added to one of the .ini files. I have never experienced stuttering when unlocking achievements on older builds of the emulator, and I find the ~2 second delay at the start of DX12 games (it's not nearly as bad on DX11 games) to be rather annoying.

[otavepto]

Some notes, here's what that will do:

• Show Achievements button will be very slow on first activation/click
• Any game (DX11/12, OpenGL, etc...) will have a micro-stutter when the image resource is uploaded to the GPU, despite what the issue states, check frame time with RivaTuner RTSS you'll notice the impact very clearly
• Test Achievement will be a gamble, whatever image it chooses that's not uploaded yet will also result in a micro-stutter

Basically, a regression in all aspects back to how it was previously, in favor of gaining literally around ~5 seconds of startup time. Just for the second reason alone (impacting gameplay) I'm tempted to reject this issue.

I'll leave it for now if someone else wants to add a flag for it, here's the relevant function https://github.com/otavepto/gbe_fork/blob/a844d85dd380d77b7936234c63e9942b34868ae5/overlay_experimental/steam_overlay.cpp#L377-L378

At the end of it, there's a flag which declares that this function has done it's job. I doesn't matter if the icons were loaded or not, it just needs to run once and loop over all achievements. https://github.com/otavepto/gbe_fork/blob/a844d85dd380d77b7936234c63e9942b34868ae5/overlay_experimental/steam_overlay.cpp#L407-L409

And that flag, impacts the overall state of the overlay https://github.com/otavepto/gbe_fork/blob/a844d85dd380d77b7936234c63e9942b34868ae5/overlay_experimental/steam_overlay.cpp#L1794-L1797