[ArrayManager] TST: activate a bunch of (passing) tests
xref https://github.com/pandas-dev/pandas/issues/39146/

This is on top of #40152, so only the second commit is relevant: https://github.com/pandas-dev/pandas/pull/40217/commits/e7209aaa7b85c206d3efcd446eaa54b34851cb98

But this basically adds the following to CI for ArrayManager:

```
        pytest pandas/tests/api/ --array-manager
        pytest pandas/tests/base/ --array-manager
        pytest pandas/tests/computation/ --array-manager
        pytest pandas/tests/config/ --array-manager
        pytest pandas/tests/dtypes/ --array-manager
        pytest pandas/tests/generic/ --array-manager
        pytest pandas/tests/indexes/ --array-manager
        pytest pandas/tests/libs/ --array-manager
        pytest pandas/tests/plotting/ --array-manager
        pytest pandas/tests/scalar/ --array-manager
        pytest pandas/tests/strings/ --array-manager
        pytest pandas/tests/tools/ --array-manager
        pytest pandas/tests/tseries/ --array-manager
        pytest pandas/tests/tslibs/ --array-manager
        pytest pandas/tests/util/ --array-manager
```
LGTM (just looked at the second commit)

for testing locally, is there a simple command i can use instead of copy/pasting the entire list of files? > is there a simple command i can use instead of copy/pasting the entire list of files?

What do you mean exactly? To only run the tests that are already activated on CI?  > What do you mean exactly? To only run the tests that are already activated on CI?

yah, ATM when i want to run the relevant ArrayManager tests i do `pytest pandas/tests/foo panda/test/bar pandas/tests/baz [...] --array-manager` and its starting to involve a lot of copy/pasting (which is a good thing!)
 can you rebase > yah, ATM when i want to run the relevant ArrayManager tests i do `pytest pandas/tests/foo panda/test/bar pandas/tests/baz [...] --array-manager` and its starting to involve a lot of copy/pasting (which is a good thing!)

Yeah, that's a little bit annoying. Most of the time I am focusing on tests in a single directory, and then that's OK. But we're getting closer to get all tests running ;)