API test failed for remote platform in
[#112657](https://github.com/llvm/llvm-project/pull/112657)

Previously when putting files onto remote platform, I used `platform
file write -d <data>` which actually required a `platform file open
<path>` first in order to obtain a file descriptor.
eg. in file
[TestGDBRemotePlatformFile.py](https://github.com/llvm/llvm-project/blob/94e7d9c0bfe517507ea08b00fb00c32fb2837a82/lldb/test/API/functionalities/gdb_remote_client/TestGDBRemotePlatformFile.py#L24-L32)
To fix this, use the `platform put-file` method, which is used in the
`redirect_stdin` from this test already.

When `FileAction` opens file with write access, it doesn't clear the
file nor append to the end of the file if it already exists. Instead, it
writes from cursor index 0.

For example, by using the settings `target.output-path` and
`target.error-path`, lldb will redirect process stdout/stderr to files.
It then calls this function to write to the files which the above
symptoms appear.

## Test
- Added unit test checking the file flags
- Added 2 api tests checking
  - File content overwritten if the file path already exists
- Stdout and stderr redirection to the same file doesn't change its
behavior

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 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

Not needed now that we require python 3.

Reviewed By: kastiglione, JDevlieghere

Differential Revision: https://reviews.llvm.org/D131761

Followup to D127355 and D127378, converting more instances of
assertEqual to assertState.

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

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

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

There is a .categories file in the python_api directory that makes all nested tests
belong to the category "pyapi". The decorator is unnecessary for these tests.

Convert `assertTrue(a == b)` to `assertEqual(a, b)` to produce better failure messages.

These were mostly done via regex search & replace, with some manual fixes.

Differential Revision: https://reviews.llvm.org/D95813