R1:0c0cbb1c09e4

Fix an issue where transactions in mail were always rendered as text

Summary:
Fixes T12921. Currently, we call `getTitleForHTMLMail()`, but that calls `getTitleForMail()` which forces us into text rendering mode.

Instead, have `getTitleForHTML/TextMail()` force the rendering mode, then call `getTitleForMail()` with the desired rendering mode.

This causes stories like "epriestely added dependent tasks: x, y." to appear as links in email instead of plain text.

Test Plan: Used `bin/mail show-outbound --id…