Rollup merge of #129191 - aDotInTheVoid:rdj-serial-cleanup, r=GuillaumeGomez

rustdoc-json: Clean up serialization and printing.

Somewhat a followup to #128963, but makes sense regardless.

- Renames `out_path` to `out_dir` because it's not the path to the JSON, but the directory
  - Also adds a comment explaining `None`
- Renames `write` to `serialize_and_write` because it does both.
  - Also renames the self-profile activity name to be clear this measures both IO cost and serialization CPU cost
  - Expands the timer to cover flushing
- Renames `output` to `output_crate`, to emphasize it's the contents, not the `--output` flag.

r? `@GuillaumeGomez`

0 files changed, 0 insertions, 0 deletions