I wanted to preserve the parameter-less constructor of tests, but WINAPI
requires fairly ugly entagled set of functions, passing HWND around,
which required storing it in a global var and hoping it is properly
initialized when querying it for it to be passed to application
constructor.
When this was done, it was now fairly easy to support passing also
argv/argc to application constructor, which in the future will enable
selective disabling of extensions for even better test coverage.
This however needed slightly different main() function and thus we now
have MAGNUM_GL_TEST_MAIN() instead of CORRADE_TEST_MAIN(). Using the
latter will result in an assert inside std::optional.
Vladimír Vondruš
88f0415290