* [examples] Add core_scissor_shape
Clip drawing to an arbitrary shape using the stencil buffer, since
BeginScissorMode() only supports axis-aligned rectangles.
* [examples] Rename to gl_scissor_shapes.c
Rename core_scissor_shape to gl_scissor_shapes, move to others. Per @raysan5's review feedback on the PR: keep OpenGL-facing examples
under examples/others, consistent with rlgl_standalone and
raylib_opengl_interop, to avoid multi-platform/build-system issues.
