Implement ToString() method for DataFrameColumn class

[asmirnov82]

Fixes #7101

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 35 lines in your changes are missing coverage. Please review.

Project coverage is 68.48%. Comparing base (214e12a) to head (e264f14).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #7103      +/-   ##
==========================================
- Coverage   68.49%   68.48%   -0.01%     
==========================================
  Files        1262     1262              
  Lines      254295   254320      +25     
  Branches    26242    26246       +4     
==========================================
- Hits       174182   174179       -3     
- Misses      73424    73450      +26     
- Partials     6689     6691       +2     

Flag	Coverage Δ
Debug	68.48% <0.00%> (-0.01%)	⬇️
production	62.88% <0.00%> (-0.01%)	⬇️
test	88.56% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

Files	Coverage Δ
...sis/DataFrameColumns/ArrowStringDataFrameColumn.cs	63.54% <0.00%> (ø)
...Analysis/DataFrameColumns/StringDataFrameColumn.cs	71.42% <0.00%> (ø)
...nalysis/DataFrameColumns/VBufferDataFrameColumn.cs	45.77% <0.00%> (ø)
...icrosoft.Data.Analysis/PrimitiveDataFrameColumn.cs	72.53% <0.00%> (+0.23%)	⬆️
src/Microsoft.Data.Analysis/Strings.Designer.cs	41.49% <0.00%> (-0.87%)	⬇️
src/Microsoft.Data.Analysis/DataFrame.cs	85.42% <0.00%> (-1.31%)	⬇️
src/Microsoft.Data.Analysis/DataFrameColumn.cs	62.83% <0.00%> (-4.32%)	⬇️

... and 2 files with indirect coverage changes

[michaelgsharp]

LGTM. Thanks!