Use strict comparison in various files

[SergeyBiryukov]

Trac ticket:
https://core.trac.wordpress.org/ticket/62279
https://core.trac.wordpress.org/ticket/61607
https://core.trac.wordpress.org/ticket/60700
https://core.trac.wordpress.org/ticket/58831
https://core.trac.wordpress.org/ticket/57839
https://core.trac.wordpress.org/ticket/56791

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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.

[aristath]

LGTM 👍

[peterwilsoncc]

This will need tests before it can be merged:

To avoid a repeat of Core-61749:

• Anything that calls WP_Query will need checks for both arrays and query string formatted arguments passed to wp_parse_args()
• Same for any of the other altered functions that use wp_parse_args()

I can see an issue with the privacy policy code breaking is_privacy_policy for one but expect there will be other issue that need testing. To reproduce the issue with the privacy policy:

1. In the dashboard create a page named Privacy Policy
2. In Settings > Privacy define the page as such
3. Run the following command in the CLI

   $ git checkout trunk
   $ wp eval "var_dump( ( new WP_Query( [ 'page_id' => 128, 'post_type' => 'page' ] ) )->is_privacy_policy );"
   :bool(true)
   $ gh pr checkout 3873 ## This branch (Sergey can use git checkout)
   $ wp eval "var_dump( ( new WP_Query( [ 'page_id' => 128, 'post_type' => 'page' ] ) )->is_privacy_policy );"
   :bool(false)
   

[SergeyBiryukov]

This will need tests before it can be merged:

Indeed, this is basically still a draft where I cherry-pick certain changes after a closer review, making sure they are covered by new or existing tests. I will investigate anything related to wp_parse_args() and WP_Query, thanks!