Desktop: Accessibility: Add missing labels and role information to several controls

[personalizedrefrigerator]

Summary

This pull request improves the accessibility of the desktop app. In particular, it,

• Marks command-based buttons as buttons — previously, they were marked as links and "disabled" wasn't read by the screen reader.
• Adds labels to buttons in the note properties dialog.
• Marks the table in the note properties dialog as a table.
• Adds labels to the "shared" and note count fields in the notebook list.
• Adds a label to the "search" and "clear search" buttons in the note list.

Manual testing

Limited manual testing has been done on MacOS:

• Verified that the the note properties dialog edit, copy, and save buttons have labels that are read by the screen reader.
• Verified that the "search" button above the note list is read as having a "search" label.
• Verified that a shared notebook is read as shared when focused in the notebook sidebar.
• Verified that a disabled command button (forward) is read as "dimmed".