This change adds new --rb-p-flag-draft-* and --rb-p-flag-published-*

definitions to our standard colour palette. These should be used for flags

that indicate whether an item is a draft or published. The colours either

exactly match the old ones that we used or are very close. We update the

following items to use these new definitions:

Comment flags
Comment tooltips
Image region comments
Datagrid draft labels
File attachment draft labels

This change also fixes a syntax mistake in the definition for

--rb-theme-rich-text-code-fg, and pulls out a couple variable

definitions for --rb-theme-rich-text-code-bg to make code blocks

in comment tooltips look nicer.

Looked at the comments, datagrid labels and file attachment labels on

darkmode and lightmode.