EES-5939 'add block/section' button focus behaviour

[Guy-HiveIT]

This PR fixes multiple focus-related issues for the release and methodology content pages.

Currently, many buttons which add items or show/close modals don't move the focus, so screen reader users can't see any change has happened, and keyboard users have to tab to access the next logical action.

• When adding a new content section, move focus to the added section accordion item, ready to expand it.
• When adding a data block to a section, move focus to the newly-appeared data block select (this change affects more places but all with this desired behaviour)
• When closing the embed URL modal on cancel or escape, move focus back to the 'Embed a URL' button
• When adding a new text block, move focus to the added block's 'Edit block' button, ready to edit the new block.