fips: Fix dlsym wrapper for egl symbols

fips: Fix dlsym wrapper for egl symbols

Previously, fips was failing to provide its own wrapped versions for
functions such as eglMakeCurrent if the application was using dlsym to
locate the symbol. This led to the failure of the egl-opengl-dlopen-*
tests in the test suite.

The root of the problem was that the fips wrapper for dlopen was only
returning the libfips_handle if dlopen was requested for
"libGL.so". But here, we need to also intercept a dlopen for
"libEGL.so" as well.

However, the fix is not as simple as updating dlopen.

Previously, if dlsym failed to find a libfips-specific version of the
symbol of interest it would defer unconditionally to a call to the
real dlsym with a handle dlopened from "libGL.so". That's obviously
the wrong thing for symbols sougth from "libEGL.so". So, now, our
dlopen caches the originally dlopen'ed handles and encodes an index
into its return value so that the final dlsym can reference the
correct handle in order to find its symbol.

This commit fixes the egl-opengl-dlopen-dlsym and
egl-opengl-dlopen-gpa test cases.