### Problem description
https://gitlab.freedesktop.org/mesa/mesa/-/issues/11135
It turns out LLVMpipe only supports 4x multisampling. Checking
GL_MAX_SAMPLES seems like the right thing to do.
### Implementation description
~~Right now, I only check GL_MAX_SAMPLES. Depending on the format, we
might need to check GL_MAX_INTEGER_SAMPLES. I don't know how likely it
is that you might want to use a different format in the future,
glGetInternalformativ might be a safer option to retrieve the max number
of samples we can use.~~
Ended up implementing it with glGetInternalformativ.
### Additional things
I guess I could merge the ```if```s at lines 95, 99 and 103 in
imgui_imhex_extensions.cpp while we're at it.
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Co-authored-by: Nik <werwolv98@gmail.com>
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