Background image: move controls into a popover (WordPress#60151)

* Testing other component layout and dummy toolspanel items
Refactor the media toggle button and refactor controls
Temp. don't send default controls in hook

* Rejigging components, catering for no-background-image-controls

* With tabs

A bit of margin

* Revert tabs and move the image upload to the floating panel

* Temp hack to push popover into the background

* Fix hack to push popover into the background

* Tweak size of media flow dropdown
Icon margin tweak

* Remove default controls override as there's only 'background image' now.
Reset image functions reset all background image properties.

isShownByDefault prop not used. Deleting

Prevent focal point picker creating horizontal scroll

Expand popover on mobile
Don't resize with window height change

* Rolling back expanding popover in mobile.
Squishing all the controls, including giving the focal point picker a max-height

* Remove commented-out code

* Revert input sizes
Ensure long file names are not cut off by min-width
Use clamp value for focal picker image height

Unlinked contributors: brentjett.

Co-authored-by: ramonjd <ramonopoly@git.wordpress.org>
Co-authored-by: andrewserong <andrewserong@git.wordpress.org>
Co-authored-by: jasmussen <joen@git.wordpress.org>
Co-authored-by: jameskoster <jameskoster@git.wordpress.org>

packages/base-styles/_z-index.scss

@@ -65,8 +65,10 @@ $z-layers: (
 	// Needs to be below media library that has a z-index of 160000.
 	"{core/video track editor popover}": 160000 - 10,
 
-	// Needs to be below media library that has a z-index of 160000.
+	// Needs to be below media library (.media-model) that has a z-index of 160000.
 	".block-editor-format-toolbar__image-popover": 160000 - 10,
+	// Below the media library backdrop (.media-modal-backdrop), which has a z-index of 159900.
+	".block-editor-global-styles-background-panel__popover": 159900 - 10,
 
 	// Small screen inner blocks overlay must be displayed above drop zone,
 	// settings menu, and movers.