wayland_egl: Defer gl symbol lookups until they're possible

wayland_egl: Defer gl symbol lookups until they're possible

Commit 2e6587a14b adds a gl extension string to glsym_evas_gl_symbols()
to prevent using functions that are provided by extensions that aren't
available in the current gl context.

However, we can't query the extension strings until after we create an egl
context.

Split the regular symbol lookup stuff from the gl symbol lookup stuff so
we can query at the appropriate time.