Revisions: slash meta values for previews

[adamsilverstein]

Correct an issue where meta values with values like a quote ” could not be previewed. update_metadata expects data to be slashed.

To test this bug:

1. publish a post with a footnote
2. add a quote to the end of the footnote
3. preview the post

expected: footnote shows quote

actual: footnote is missing or missing quote

Trac ticket: https://core.trac.wordpress.org/ticket/20564

See also: WordPress/gutenberg#52988

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This Pull Request is for code review only. Please keep all other discussion in the Trac ticket. Do not merge this Pull Request. See GitHub Pull Requests for Code Review in the Core Handbook for more details.

[mukeshpanchal27]

@adamsilverstein, If we remove the wp_slash, the unit tests pass successfully ✅. Do we still need to implement safeguard measures?

[mukeshpanchal27]

Thanks @adamsilverstein for the PR. Approved with one question: #5344 (comment)

[adamsilverstein]

@adamsilverstein, If we remove the wp_slash, the unit tests pass successfully ✅. Do we still need to implement safeguard measures?

I added a test that failed before the patch, but removed it to get tests passing in 6927209 because it was causing other tests to fail (I suspect because it wasn't cleaning up completely). I'm going to try to reintroduce it in another spot.

[adamsilverstein]

@mukeshpanchal27 - I reintroduced the test by putting it in the metaRevisions test file and cleaning it up a bit. This test fails before the PR and essentially reproduces the issue surfaced by the GB E2E test.

[adamsilverstein]

Trying again in 413ac9f (#5344); I moved the tests to tests/phpunit/tests/rest-api/rest-autosaves-controller.php and simplified a bit.

[adamsilverstein]

Fixed in https://core.trac.wordpress.org/changeset/56745