Update on "[WIP] Update backward definition for more operators and reenable tests in test_ops.py"
This PR:
1. updates backward formula for the following functions: `asin`, `acos`, `asinh`, `acosh`, `atan`, `atanh`, `div`, `log`, `log10`, `log2`, `log1p`, `pow`.
2. Re-enables the tests in `test_ops.py`.
3. Fixes a bug in `.pow()` for the case when exp is complex and equals 1.0 https://github.com/pytorch/pytorch/pull/44444/files#diff-9fa1985487308c7241bba078a8622c44L33 .
4. Adds dispatch for complex dtypes for `tanh`.
5. Re-enables commented tests in `common_methods_invocation.py`.
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