R1:b75a4151c899

Allow the fulltext index to select only transactions with comments

Summary:
Ref T12997. Although we can't query by transaction type (since we can't easily enumerate all possible types which may have comments -- inline types may also have comments), we //can// just check if there's a comment row or not.

This reduces the amount of garbage we need to load to rebuild indexes for unusual objects with hundreds and hundreds of mentions.

Test Plan:
- Used batch editor to mention a task 700 times.
- Indexed…