[quant][eagermode][refactor] Add set/get method for quantization and fusion mappings (#43990)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43990
Allow user to register custom quantization and fusion patterns
Test Plan: Imported from OSS
Reviewed By: z-a-f
Differential Revision: D23485344
fbshipit-source-id: 4f0174ee6d8000d83de0f73cb370e9a1941d54aa
