Advanced Export features

[jonnywatersbb]

Adds export features to Themer under a new page, to export database changes, theme.json, patterns and templates

[g-elwell]

PR for improving theme.json/style export #124

PR for 'template manager' where you can see which block templates are pulling from the database and which are pulling from files, then reset/export data #125

For patterns, can someone add extra context around synced/unsynced, what is possible to edit and what we'd like to see within themer (if anything) to aid in managing these? Testing on the latest WP version my experience is that patterns which have a file cannot be edited - you need to duplicate them into the database, therefore there is no sync issue between files/database like we have on templates or with the theme.json values.