fix-up R parser bug in get_source_expressions

[MichaelChirico]

Split off from #1032 because in principle it could affect the logic whenever STR_CONST is involved (especially, it's probably needed as part of #1034)

[MichaelChirico]

Adding a NEWS bullet and tests...

[AshesITR]

Will this fix the xml as well? I suppose no, just wanted to confirm.

[MichaelChirico]

Yes it will, because xmlparsedata builds from the parsed data.frame if we pass on.

Here we pass the data.frame:

lintr/R/utils.R

Line 99 in 49fd346

tryCatch(xml2::read_xml(xmlparsedata::xml_parse_data(parsed_content)), error = function(e) NULL)

Here xmlparsedata builds off the data.frame it receives instead of running utils::getParseData() again:

https://github.com/r-lib/xmlparsedata/blob/ee6a15f0b9162e2d215635d9771dc5c09d3eacbf/R/package.R#L65

(this is why the other touch-ups, i.e. for tabs and equals signs, are also reflected on the XML tree we get back from xml_parse_data())