syntax: sh: Add here document as string region

[JoeKar]

This will treat a here document block with the limit string EOF as a string region.

Fixes #2949

[JoeKar]

Further discussion/suggestions have been done here: #2949

The suggestion was to allow the usual and normal characters after << till $ as start marker and do the same for end marker with ^ till $. This would allow user defined "heredoc" marker other than EOF too, but highlights event then when start != end limit string. Like below:

start: "<<[^\\s]+[-~.]*[A-Za-z0-9]+$"
end: "^[^\\s]+[A-Za-z0-9]+$"

[zyedidia]

Yeah unfortunately the current highlighting engine is not powerful enough to handle heredocs properly. This is fine for handling the common case though. I would be fine with the extended version that matches even if the start/end don't match.

[JoeKar]

I would be fine with the extended version that matches even if the start/end don't match.

Done.