Generate selective_mobile_ops.h file for executorch (#1021)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/1021

Generate `selective_mobile_ops_executorch.h`

Test using an expecttest. Check cases where we have multiple dtypes and default case (return true).

Reviewed By: JacobSzwejbka

Differential Revision: D49236461

fbshipit-source-id: 8e229313cc0d3e7175d99b42b9f036203a7808ab