Gutenberg: fix console errors and warnings

[vindl]

If you navigate to /gutenberg/post/{siteSlug} now you'll notice a couple of console warnings that need to be investigated and fixed:

• Components package: Warning: Unsafe lifecycle methods were found within a strict-mode tree: (Components package: deprecated lifecycle method warning in slot-fill WordPress/gutenberg#9017)
• Editor package: Warning: validateDOMNesting(...): <button> cannot appear as a descendant of <button>. (Editor package: invalid DOM nesting in PostPublishPanelToggle component WordPress/gutenberg#9033)
• Editor package: Warning: Unsafe lifecycle methods were found within a strict-mode tree: (Editor package: deprecated lifecycle method warning in TinyMCE WordPress/gutenberg#9037)
• When adding a new block - Uncaught (in promise) TypeError: Cannot read property 'rest_base' of undefined - I believe this is related to mocked API response for wp/v2/types and should be resolved in Gutenberg: enable v2 API requests #26639.
• When adding a new block - Uncaught SyntaxError: Unexpected token <. (Gutenberg: fix list block indent/outdent functionality #27877)

[vindl]

I started an issue in Gutenberg repo to resolve the deprecated lifecycle warning, since it's coming from the Components package: WordPress/gutenberg#9017

[vindl]

One more issue in Gutenberg repo for invalid DOM nesting in editor package: WordPress/gutenberg#9033