This is NFC, I'm modernizing the interface before I add to it in a
subsequent commit.

This uses [teyit](https://pypi.org/project/teyit/) to modernize asserts,
as recommended by the [unittest release
notes](https://docs.python.org/3.12/whatsnew/3.12.html#id3).

For example, `assertTrue(a == b)` is replaced with `assertEqual(a, b)`.
This produces better error messages, e.g. `error: unexpectedly found 1
and 2 to be different` instead of `error: False`.

This reverts commit 6ea1a0d4fc3823de143a288df2059b48dc01cf72.

It again marks XFAIL LLDB tests failing after
c384fcd3ea1dad782eaaea89b32fc33c0c3528b8

This is an ongoing series of commits that are reformatting our Python
code. Reformatting is done with `black` (23.1.0).

If you end up having problems merging this commit because you have made
changes to a python file, the best way to handle that is to run `git
checkout --ours <yourfile>` and then reformat it with black.

RFC: https://discourse.llvm.org/t/rfc-document-and-standardize-python-code-style

Differential revision: https://reviews.llvm.org/D151460

This patch add or removes XFAIL decorator from various tests which were marked
xfail for windows.

since 44363f2 various tests have started passing but introduced a couple of new failures.
Weight is in favor of new XPasses and I have removed XFail decorator from them. Also
some new tests have started failing for which we need to file separate bugs. I have
marked them xfail for now and will add the bug id after investigating the issue.

Differential Revision: https://reviews.llvm.org/D149235

Eliminate boilerplate of having each test manually assign to `mydir` by calling
`compute_mydir` in lldbtest.py.

Differential Revision: https://reviews.llvm.org/D128077

Replace forms of `assertTrue(err.Success())` with `assertSuccess(err)` (added in D82759).

* `assertSuccess` prints out the error's message
* `assertSuccess` expresses explicit higher level semantics, both to the reader and for test failure output
* `assertSuccess` seems not to be well known, using it where possible will help spread knowledge
* `assertSuccess` statements are more succinct

Differential Revision: https://reviews.llvm.org/D119616

This patch removes the infrastructure to replay the test suite from a
reproducer, as well as the modifications made to the individual tests.