[Renderers/Examples] Move raylib renderer to single header

[peterc-s]

As discussed on discord, to use Clay with the raylib renderer with GNU Make and GCC you had to separate out implementation from the raylib_renderer_raylib.c into a header file and make a few other changes.

I've moved the whole renderer into a single header file and this seems to work without any of those modifications needing to be made.

I've also fixed a segfault in the video example by copying over the minimum memory allocation from the raylib sidebar scrolling example.

[peterc-s]

Sorry, realised my git was misconfigured and so commits came up as unverified so had to rebase and force push to sign them properly.

[ThreedResident]

Any chance all this will be merged to main soon?