Profiler: Cache and reuse mapped ELF objects

In multi-process profiles, the same ELF objects tend to occur many
times (everyone has libc.so for example) so we will quickly run out
of VM if we map each object once per process that uses it.

Fix this by adding a "mapped object cache" that maps the path of
an ELF object to a cached memory mapping and wrapping ELF::Image.

Userland/DevTools/Profiler/DisassemblyModel.cpp

@@ -74,7 +74,7 @@ DisassemblyModel::DisassemblyModel(Profile& profile, ProfileNode& node)
             dbgln("no library data");
             return;
         }
-        elf = &library_data->elf;
+        elf = &library_data->object->elf;
         base_address = library_data->base;
     }