Blocks: Remove obsolete isSelected usage (part 3)

[gziolo]

Description

Closes #5633.

Follow up for #5029, #6201 and #6248.

isSelected usage is no longer mandatory with BlockControls, InspectorControls and RichText. It's now handled by the editor internally to ensure that controls are visible only when the block is selected.

Refactored blocks:

• Preformatted
• Pullquote
• Quote
• Tabel
• Text columns
• Subhead
• Verse
• Video

This covers all core blocks 🎉

When updating Text columns block I also fixed the following issue reported in #5633:

The Text Columns block allows to create text over N columns. When creating a Text Columns block with 3 columns, and you attempt to change the formatting of the text in one column (i.e. add a link, make bold, etc), the text formatting toolbar appears 3 times. Furthermore, when adding a link, the "add link" popup will appear three times. This issue also scales, so when creating 5 columns, the formatting toolbar will show 5 times

It should be much easier to review this diff without whitespace changes:

https://github.com/WordPress/gutenberg/pull/6280/files?w=1

How has this been tested?

Manually, unit tests and e2e tests.

Types of changes

Refactoring, no visual changes.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.

[jorgefilipecosta]

Changes here look good to me 👍 I did a set of smoke tests in all the changed blocks and I did not noticed regressions :)