Update on "rename slimtensor fiies to consistent with executorch files"

This diff updates the slimtensor file names to follow ET style (use under_score instead of Camel).
Note that we keep the c10 files as Camel since et/c10 files are also in Camel Case.

Differential Revision: [D90143740](https://our.internmc.facebook.com/intern/diff/D90143740/)

[ghstack-poisoned]

Author: Gasoonjia

backends/aoti/slim/core/test/test_slimtensor_copy.cpp

@@ -11,7 +11,6 @@
 #include <executorch/backends/aoti/slim/core/slim_tensor.h>
 #include <executorch/backends/aoti/slim/core/storage.h>
 
-
 namespace executorch::backends::aoti::slim {
 
 // Helper function to create a CPU storage with given size