Update base for 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