Make "metamta.differential.inline-patches" imply a reasonable byte limit, not just a line limit

Summary:
Fixes T11748. This option currently implies a line limit (e.g., inline patches that are less than 100 lines long). This breaks down if a diff has a 10MB line, like a huge blob of JSON all on one line.

For now, imply a reasonable byte limit (256 bytes per line).

See T11767 for future work to make this and related options more cohesive.

Test Plan:

• With option at 1000: sent Differential email, saw patches inlined.
• With option at 10: sent Differential email, saw patches dropped because of the byte limit.
• var_dump()'d the actual limits and used bin/worker execute --id ... to sanity check that things were working properly.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11748

Differential Revision: https://secure.phabricator.com/D16714