R1:2025ecd3d826

Rough cut of inline comment context

Summary:
Ref T10694. This is still missing some pieces, but seems to get most of the data into the mail in a plausible format:

- When an inline remarks on code, show the patch inline in the mail body.
- When an inline replies to another inline, show that other inline in the mail body.
- Apply remarkup rendering to inline content.
- Apply basic styling to mail body blocks.

Not covered yet:

- Syntax highlighting.
- Diff highlighting.
- Maybe clearer…