R1:0d01dab5a375

Partially revert D14511 to fix "INLINE COMMENTS" in mail

Summary:
Ref T9845. In Differential, this is not a remarkup block -- it's a mail section. `addTextSection()` has special magic behavior when handed a prebuilt section since D9375.

Swapping to `addRemarkupSection()` causes the error in T9845 and renders nothing in the comment section.

Even if it were a block of text, it would not be appropriate to add it as remarkup. This would incorrectly render comments in files like `__init__.py`, which are…