Fixes: #40204

What?

• Adds new Gutenberg Experiment to put the new tabs feature behind
• Splits the block inspector primarily between settings and appearance-related tools.
• The appearance tab contains tools provided via block supports.
• The settings tab contains block-specific tools rendered into the default InspectorControls slot.
• Updates the sidebar icon to use two new "drawer" icons taking into account RTL.

Why?

It's another step towards decluttering the sidebar and making it more intuitive to locate and discover block tools.

How?

• Adds new drawer icons to the icons package
• Updates sidebar icons
• Updates the TabPanel component to allow icon-only buttons
• Adds Gutenberg Experiment, making the new tabs opt-in
• Updates the block inspector to render the various InspectorControls slots into their respective tabs when the new experiment is enabled
• The same tabs have been introduced into the block inspector for both single and multi-block selections

Note: Tabs are no longer omitted should they not have any fills in their respective slots. Instead, they'd display a message illustrating the fact there are no settings/appearance tools. This helps maintain a more consistent UI for a11y purposes.

Testing Instructions

1. Check that the sidebar icons have been updated in both the post and site editors, and confirm they get flipped when switching between LTR and RTL.
2. In the post editor, add a navigation block, several paragraphs, a group block etc., to a post, save and select one.
3. Confirm the block inspector displays as normal.
4. Navigate to the Gutenberg Experiments admin page and enabled the Block Inspector Tabs experiment
   
5. Switch back to the editor, reload the page, and select each block.
6. Check that both tabs (settings & appearance) are in the sidebar and controls continue to function.
7. Select multiple blocks of different types and confirm no controls within either tab.
8. Select multiple blocks of the same type, e.g. two paragraph blocks. The appearance tab should still contain items.

Screenshots or screencast