API: Series and DataFrame constructors to return shallow copy (i.e. don't share index) from another Series/DataFrame
This changes the Series and DataFrame constructors to return a proper shallow copy (i.e. only share data, not attributes like the index) instead of returning a new Series/DataFrame object but with the same manager, for the case of `Series(s)` or `DataFrame(df)` (so no reindexing or casting, and with default of `copy=False`).

See https://github.com/pandas-dev/pandas/issues/49523 for an example.

Strictly speaking this is a breaking change (or notable bug fix, not sure if this was done intentionally in the past).

- [ ] closes #49523
- [ ] [Tests added and passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#writing-tests) if fixing a bug or adding a new feature
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added [type annotations](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#type-hints) to new arguments/methods/functions.
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

@jbrockmendel good to go? LGTM merge on green