Use dedicated PathElement for values provided manually

[MateuszKubuszok]

When using:

• withFieldConstPartial
• withFieldCompured (in PartialTransformer)
• withFieldComputedPartial

we were just prepending to the Path the PathElement.Accessor with the name of the currently handled target field. But the Path is designed to handle path from source value. In nested data this results in a chain of fields where the prefix comes from source type and the last field from the target type. It makes no sense.

This PR introduces a dedicated PathElement for storing errors from provided values, which may not have source or their source may be unrelated to the currently used From expression.

[codecov]

Codecov Report

Attention: Patch coverage is 94.33962% with 3 lines in your changes missing coverage. Please review.

Project coverage is 85.94%. Comparing base (d5a6588) to head (e17d86b).
Report is 3 commits behind head on master.

Files with missing lines	Patch %	Lines
...er/rules/TransformProductToProductRuleModule.scala	94.11%	2 Missing ⚠️
...ala/io/scalaland/chimney/partial/PathElement.scala	75.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #655      +/-   ##
==========================================
+ Coverage   85.82%   85.94%   +0.12%     
==========================================
  Files         160      160              
  Lines        6715     6680      -35     
  Branches      560      559       -1     
==========================================
- Hits         5763     5741      -22     
+ Misses        952      939      -13     

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.