Emacs: Ensure left-to-right display for message headers

Emacs: Ensure left-to-right display for message headers

In notmuch-show buffer insert invisible U+200E LEFT-TO-RIGHT MARK
character at the beginning of message header paragraph if the From
header contains a right-to-left character. This ensures that the
header paragraph is always rendered in left-to-right mode.

See Emacs Lisp reference manual section "(elisp) Bidirectional
Display" for more info.