libsysprof: add versioning macros

This also moves stackstash.[ch] into a location that can be
embedded by both the libsysprof and libsysprof-ui code. We
pass native pointers to the structure as a gpointer in the
public API to allow for this. The performance of that code is
incredibly sensitive to the interactivity of Sysprof.

src/libsysprof-ui/meson.build

@@ -23,6 +23,7 @@ libsysprof_ui_private_sources = [
   'rectangles.c',
   'sp-cell-renderer-percent.c',
   'sp-theme-manager.c',
+  '../stackstash.c',
 ]
 
 libsysprof_ui_public_headers = [