private BookmarkDB getBookmark(DBRecord bookmarkRecord) {
		BookmarkDB bm = cache.get(bookmarkRecord);
		if (bm == null) {
			bm = new BookmarkDB(this, cache, bookmarkRecord);
		}
		return bm;
	}
Update stored bookmark and fire program change event for a bookmark which has
had its category or comment changed.  All other fields are immutable.
@param bm bookmark
Ghidra/Framework/SoftwareModeling/src/main/java/ghidra/program/database/bookmark/BookmarkDBManager.java