Writing settings: Add "Default post category" selector

[mmtr]

Part of #95621
See pekYwv-4RI-p2

Proposed Changes

Adds a new dropdown to the Writing Settings page to change the default post category so users can follow Core tutorials instructing them to go to "Settings > Writing" to do so.

Why are these changes being made?

Because we don't want users participating in the "Remove duplicate views" projects to be forced to use /wp-admin/options-writing.php to change the default category, since we're not untangling the Writing Settings page in the short/mid term.

Testing Instructions

• Use the Calypso live link below
• Go to /settings/writing/:site
• Make sure you can change the default post category
• Make sure the changes are reflected in /wp-admin/edit-tags.php?taxonomy=category and in /wp-admin/options-writing.php.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
  • For UI changes, have we tested the change in various languages (for example, ES, PT, FR, or DE)? The length of text and words vary significantly between languages.
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128009

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128009&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-128009&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

App Entrypoints (~2 bytes added 📈 [gzipped])

name                 parsed_size           gzip_size
entry-subscriptions        +17 B  (+0.0%)       +2 B  (+0.0%)
entry-stepper              +17 B  (+0.0%)       +2 B  (+0.0%)
entry-main                 +17 B  (+0.0%)       +2 B  (+0.0%)
entry-login                +17 B  (+0.0%)       +2 B  (+0.0%)

Common code that is always downloaded and parsed every time the app is loaded, no matter which route is used.

Sections (~168 bytes added 📈 [gzipped])

name                 parsed_size           gzip_size
settings-writing          +805 B  (+0.1%)     +168 B  (+0.1%)
settings-podcast           +11 B  (+0.0%)       +4 B  (+0.0%)
settings-newsletter        +11 B  (+0.0%)       +4 B  (+0.0%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug add/settings-writing-default-post-category on your sandbox.

[rcrdortiz]

Changes look good and test well.

[a8ci18n]

This Pull Request is now available for translation here: https://translate.wordpress.com/deliverables/17069189

Some locales (Hebrew, Japanese) have been temporarily machine-translated due to translator availability. All other translations are usually ready within a few days. Untranslated and machine-translated strings will be sent for translation next Monday and are expected to be completed by the following Friday.

Thank you @mmtr for including a screenshot in the description! This is really helpful for our translators.

[a8ci18n]

Translation for this Pull Request has now been finished.