Review button bar component and pattern guidance

[navkaur76]

Review button bar pattern site guidance (and examples), and update to reflect amended stance on ordering of buttons. Also consider the recent button work.

Figma work to be done (in both Next + Legacy):

• Add new button bar set with updated styling and button ordering
• Update pattern page examples and guidance. Add a note at the end of the page for option to use solid neutral button as an alternative secondary action (for MTK)
• Implement deprecation as component set

@bhoppers2008 to address #3933 for any pending updates to be made in Light/Dark libraries

[mark-tate]

Latte Goal: complete, requires review by EOS

[bhoppers2008]

No work to happen beyond pushing dialog header to labs in Latte. Updates to dialog core examples and guidance and button bar pattern page to be updated for core in Lungo sprint.