Run the formatter on paste

[SCWells72]

The LSP formatter should be run automatically on the pasted text range when code is pasted into an LSP4IJ-managed file.

[SCWells72]

I'm happy to take this one. I'm actually a little surprised that it's not just happening auotmatically.

[SCWells72]

Debugging this a bit, it's happening for a few reasons. First, the default behavior for format-on-paste is to indent each line and not perform full range formatting:

and LSP4IJ doesn't include a lineIndentProvider implementation...which might be tricky anyway as I think it would require execution of the formatter and then applying only the line indentation edits and not other formatting changes.

I had hoped that it would just work by changing that IDE config option to Reformat block, but unfortunately it doesn't because of the following in PasteHandler#doPasteAction():

if (LanguageFormatting.INSTANCE.forContext(file) == null && indentOptions != CodeInsightSettings.NO_REFORMAT) {
  indentOptions = CodeInsightSettings.INDENT_BLOCK;
}

LSP4IJ implements formattingService but not lang.formatter, so LanguageFormatting#forContext() returns null for TextMate and plain text files typically used by LSP4IJ. As a result, it once again tries to apply indentation and...well...see above.

I see a few primary options for this:

1. Implement lineIndentProvider as described above, applying only the text edits that represent indentation changes. By itself, that would have the effect of always adjusting line indents even if configured to reformat the block. This would also add first-class support for the IDE's Auto-Indent Lines action, so it's not just beneficial for reformat-on-paste.
2. Implement copyPastePostProcessor to reformat the pasted text range if Reformat on paste is configured to anything but None. By itself, that would have the effect of always formatting on paste even if configured to adjust line indents only.
3. A hybrid of these two where the lineIndentProvider would properly handle adjusting line indents on paste and the copyPastePostProcessor would only kick in if Reformat on paste is set to Reformat block.
4. Actually implement lang.formatter, though I'm not sure what that means when there's already a formattingService implementation. My guess is that this option is the least viable/attractive of the bunch.

And there's always the problem of language servers that support full file reformatting but not range formatting, or that support range formatting but poorly. Those require a bit more thought if they're also to be supported...

Anyway, just capturing thoughts/findings while they're fresh in my head...