…json

[1] will enable sub projects inheriting parent's `spec.src.json`,
in order to generate similar but subtlely different tests.
As a preparation for [1],
this CL centralizes per-project configs into `spec.src.json`,
by moving config values from per-project `generate.py` into `spec.src.json`.

- `spec_directory` is now the current directory,
  or specified by the `--spec` command line option,
  while previously it is calculated based on the per-project `generate.py`'s path.
- Script paths (`helper_js`, `sanity_checker_js`, `spec_json_js`) are now hard-coded
  (using `spec_directory`) in `common/security-features/tools/generate.py`.
- Other config values are moved into `spec.src.json`.
- `spec_json.js` is moved under `generic/`, to a little centralize
  generator-related files into `generic/`.

Generated files are affected because:

- Scripts (like `test-case.sub.js`) are now referenced as relative paths
  from generated test HTMLs.
- `disclaimer.template` is updated.

Generated files will be updated in a separate CL [2].

[1] https://chromium-review.googlesource.com/c/chromium/src/+/1991066/
[2] https://chromium-review.googlesource.com/c/chromium/src/+/1992955/

Bug: 906850
Change-Id: Id3b2a26b67296a1de2b682e07bdcf473f666cd25
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1989718
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Cr-Commit-Position: refs/heads/master@{#731858}