Merge trunk into merge/18.9-into-trunk

Conflicts in all the `*.lproj/Localizable.strings` from the
WordPressShareExtension and WordPressTodayWidget targets. The conflicts
are a byproduct of the work done in
#17630 and
#17636.

I haven't spent the time to research why Git saw those a modified on
`trunk` because, regardless, the right thing for them is to be deleted
now that the extensions fetch their strings from the main bundle.

Also got a conflict on the `ar-SA` release notes. I resolved it by
keeping the more recent version from 19.0.

Full list of conflicting files:

```
WordPress/WordPressShareExtension/ar.lproj/Localizable.strings
WordPress/WordPressShareExtension/bg.lproj/Localizable.strings
WordPress/WordPressShareExtension/cs.lproj/Localizable.strings
WordPress/WordPressShareExtension/cy.lproj/Localizable.strings
WordPress/WordPressShareExtension/da.lproj/Localizable.strings
WordPress/WordPressShareExtension/de.lproj/Localizable.strings
WordPress/WordPressShareExtension/en-AU.lproj/Localizable.strings
WordPress/WordPressShareExtension/en-CA.lproj/Localizable.strings
WordPress/WordPressShareExtension/en-GB.lproj/Localizable.strings
WordPress/WordPressShareExtension/es.lproj/Localizable.strings
WordPress/WordPressShareExtension/fr.lproj/Localizable.strings
WordPress/WordPressShareExtension/he.lproj/Localizable.strings
WordPress/WordPressShareExtension/hr.lproj/Localizable.strings
WordPress/WordPressShareExtension/hu.lproj/Localizable.strings
WordPress/WordPressShareExtension/id.lproj/Localizable.strings
WordPress/WordPressShareExtension/is.lproj/Localizable.strings
WordPress/WordPressShareExtension/it.lproj/Localizable.strings
WordPress/WordPressShareExtension/ja.lproj/Localizable.strings
WordPress/WordPressShareExtension/ko.lproj/Localizable.strings
WordPress/WordPressShareExtension/nb.lproj/Localizable.strings
WordPress/WordPressShareExtension/nl.lproj/Localizable.strings
WordPress/WordPressShareExtension/pl.lproj/Localizable.strings
WordPress/WordPressShareExtension/pt-BR.lproj/Localizable.strings
WordPress/WordPressShareExtension/pt.lproj/Localizable.strings
WordPress/WordPressShareExtension/ro.lproj/Localizable.strings
WordPress/WordPressShareExtension/ru.lproj/Localizable.strings
WordPress/WordPressShareExtension/sk.lproj/Localizable.strings
WordPress/WordPressShareExtension/sq.lproj/Localizable.strings
WordPress/WordPressShareExtension/sv.lproj/Localizable.strings
WordPress/WordPressShareExtension/th.lproj/Localizable.strings
WordPress/WordPressShareExtension/tr.lproj/Localizable.strings
WordPress/WordPressShareExtension/zh-Hans.lproj/Localizable.strings
WordPress/WordPressShareExtension/zh-Hant.lproj/Localizable.strings
WordPress/WordPressTodayWidget/ar.lproj/Localizable.strings
WordPress/WordPressTodayWidget/bg.lproj/Localizable.strings
WordPress/WordPressTodayWidget/cs.lproj/Localizable.strings
WordPress/WordPressTodayWidget/cy.lproj/Localizable.strings
WordPress/WordPressTodayWidget/da.lproj/Localizable.strings
WordPress/WordPressTodayWidget/de.lproj/Localizable.strings
WordPress/WordPressTodayWidget/en-AU.lproj/Localizable.strings
WordPress/WordPressTodayWidget/en-CA.lproj/Localizable.strings
WordPress/WordPressTodayWidget/en-GB.lproj/Localizable.strings
WordPress/WordPressTodayWidget/es.lproj/Localizable.strings
WordPress/WordPressTodayWidget/fr.lproj/Localizable.strings
WordPress/WordPressTodayWidget/he.lproj/Localizable.strings
WordPress/WordPressTodayWidget/hr.lproj/Localizable.strings
WordPress/WordPressTodayWidget/hu.lproj/Localizable.strings
WordPress/WordPressTodayWidget/id.lproj/Localizable.strings
WordPress/WordPressTodayWidget/is.lproj/Localizable.strings
WordPress/WordPressTodayWidget/it.lproj/Localizable.strings
WordPress/WordPressTodayWidget/ja.lproj/Localizable.strings
WordPress/WordPressTodayWidget/ko.lproj/Localizable.strings
WordPress/WordPressTodayWidget/nb.lproj/Localizable.strings
WordPress/WordPressTodayWidget/nl.lproj/Localizable.strings
WordPress/WordPressTodayWidget/pl.lproj/Localizable.strings
WordPress/WordPressTodayWidget/pt-BR.lproj/Localizable.strings
WordPress/WordPressTodayWidget/pt.lproj/Localizable.strings
WordPress/WordPressTodayWidget/ro.lproj/Localizable.strings
WordPress/WordPressTodayWidget/ru.lproj/Localizable.strings
WordPress/WordPressTodayWidget/sk.lproj/Localizable.strings
WordPress/WordPressTodayWidget/sq.lproj/Localizable.strings
WordPress/WordPressTodayWidget/sv.lproj/Localizable.strings
WordPress/WordPressTodayWidget/th.lproj/Localizable.strings
WordPress/WordPressTodayWidget/tr.lproj/Localizable.strings
WordPress/WordPressTodayWidget/zh-Hans.lproj/Localizable.strings
WordPress/WordPressTodayWidget/zh-Hant.lproj/Localizable.strings
fastlane/metadata/ar-SA/release_notes.txt
```

fastlane/metadata/ar-SA/keywords.txt

@@ -1 +1 @@
-اجتماعي,ملاحظات,jetpack,كتابة,وسم جغرافي,وسائط,موقع ويب,موقع إلكتروني,تدوين,مجلة
+اجتماعي,ملاحظات,jetpack,كتابة,وسم جغرافي,وسائط,موقع ويب,موقع إلكتروني,تدوين,مجلة

fastlane/metadata/es-MX/subtitle.txt

@@ -1 +1 @@
-Crear una web o un blog
+Crear una web o un blog