Move the blob page Edit button from the blob header to the title area

Context

Move 'Edit' page from the top bar of the file viewer to the blob page header area.

Current blob page	Redesigned blob page	Redesigned blob page: smaller viewports

Notes

• The old Blame button at the top of the page will be shown until performance issues are fixed with the new Blame button that appears in context of the code content. See #441773 (comment 2162244787).
• On mobile, the following functions available on Desktop will move to the 3-dot overflow menu:
  • Find file
  • Blame (old Blame button)
  • Copy file contents
  • Open raw
  • Download