file path detection in paste_linter

[MichaelChirico]

Part of #884 and #1108. We wrote this as a separate PasteFilePathLinter(), but I believe it fits well as an extension of paste_linter().

[codecov-commenter]

Codecov Report

Merging #2074 (0c5dc5d) into main (781a18d) will increase coverage by 0.00%.
The diff coverage is 100.00%.

❗ Current head 0c5dc5d differs from pull request most recent head a1bc413. Consider uploading reports for the commit a1bc413 to get more accurate results

@@           Coverage Diff           @@
##             main    #2074   +/-   ##
=======================================
  Coverage   99.64%   99.64%           
=======================================
  Files         117      117           
  Lines        5038     5106   +68     
=======================================
+ Hits         5020     5088   +68     
  Misses         18       18           

Files Changed	Coverage Δ
R/methods.R	100.00% <100.00%> (ø)
R/paste_linter.R	100.00% <100.00%> (ø)
R/xp_utils.R	100.00% <100.00%> (ø)