Refactor interface between backend and frontend (#530)

* Rename to use Config, rather than StateHandle/Globals/Backend
* Make Backend a type on Config that contains the address space management implementation
* Make Ranges part of the Backend configuration, so we can reuse code for different ways of managing memory
* Pull the common chains of range definitions into separate files for reuse.
* Move PagemapEntry to CommonConfig
* Expose Pagemap through backend, so frontend doesn't see Pagemap directly
* Remove global Pal and use DefaultPal, where one is not pass explicitly.

Co-authored-by: David Chisnall <davidchisnall@users.noreply.github.com>
Co-authored-by: Nathaniel Filardo <105816689+nwf-msr@users.noreply.github.com>

src/test/perf/singlethread/singlethread.cc

@@ -60,7 +60,7 @@ void test_alloc_dealloc(size_t count, size_t size, bool write)
     }
   }
 
-  snmalloc::debug_check_empty<Globals>();
+  snmalloc::debug_check_empty<StandardConfig>();
 }
 
 int main(int, char**)