Bug 1615937 [wpt PR 21826] - [WPT/common/security-features] Transition `spec.src...

Bug 1615937 [wpt PR 21826] - [WPT/common/security-features] Transition `spec.src.json` to JSON5, a=testonly

Automatic update from web-platform-tests
[WPT/common/security-features] Transition `spec.src.json` to JSON5

To allow inline comments in `spec.src.json` to make it more
descriptive, this CL parses `spec.src.json`s as JSON5,
using `json5` non-standard library.
After parsing, we still use `json` module for outputting
JSON objects.

Subsequent CLs e.g. [1] will actually add inline comments
to `spec.src.json`s.

[1] https://chromium-review.googlesource.com/c/chromium/src/+/2049953

This CL doesn't change the generated results.

Bug: 906850, https://github.com/web-platform-tests/wpt/issues/21824
Change-Id: I8c6472b41ae55a051889fc29cf57d392ef60b69f
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2058706
Commit-Queue: Hiroshige Hayashizaki <hiroshige@chromium.org>
Reviewed-by: Hiroki Nakagawa <nhiroki@chromium.org>
Reviewed-by: Mike West <mkwst@chromium.org>
Reviewed-by: Kenichi Ishibashi <bashi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#741850}

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wpt-commits: 8205a7e07caf3606abed03306d5b51c0d688252a
wpt-pr: 21826