[lldb] Fix write only file action to truncate the file (#112657)

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

0 files changed, 0 insertions, 0 deletions