scanner: fix position calculation for literal, folded and raw folded strings

[efd6]

The approach to calculating the column is not ideal from an allocations perpective, but is similar to other calculations in the code base that do a temporary []rune → string conversion. I would prefer to retain an offset field instead, but that is a more invasive change.

The setting of token.Position.IndentNum is left as is since it's not clear to me what that is there for; the field is never read in the code base and so is apparently not used internally (removal does not affect tests, though external client code may be using it for something).

Fixes #326.

Please take a look.

[codecov-commenter]

Codecov Report

Merging #330 (358b0ba) into master (dc3fed8) will not change coverage.
The diff coverage is n/a.

Additional details and impacted files

@@           Coverage Diff           @@
##           master     #330   +/-   ##
=======================================
  Coverage   75.63%   75.63%           
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  Files          13       13           
  Lines        4359     4359           
=======================================
  Hits         3297     3297           
  Misses        819      819           
  Partials      243      243           

[goccy]

Thank you for your great PR !!! LGTM