* Now loads context on background threads.
- For file and directory context, buffer ropes can be shared between
threads as they are immutable. This allows for traversal and
accumulation of buffer text on a background thread.
- For url context, the request, parsing, and rendering is now done on a
background thread.
* Prepares for support of buffer reload by individually storing the text
of directory buffers.
* Avoids some string copying / redundant strings.
- When attaching message context, no longer builds a string for each
context type.
- For directory context, does not build a `SharedString` for the full
text, instead has a slice of `SharedString` chunks which are then
directly appended to the message context.
- Building a fenced codeblock for a buffer now computes a precise
capacity in advance.
Release Notes:
- N/A
0dd7ea4575