Make copyFile copy symbolic links by value rather than reference

[elharo]

This restores the behavior of the copyFile methods in currently released versions. I'm 50/50 on whether this is what should be done if this method were new, but since i can see both sides I think backwards compatibility wins. Arguably this is the behavior that was documented for this method already, but I've tried to be more explicit about that in the doc comments.

copyDirectory is still under consideration. This PR does not change how that method currently behaves at HEAD. If we decide to do that, it can be handled in a separate PR.

@garydgregory @eamonnmcmanus

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 50.00000% with 1 line in your changes missing coverage. Please review.

Project coverage is 86.00%. Comparing base (5e8fdba) to head (cea0f31).
Report is 980 commits behind head on master.

Files with missing lines	Patch %	Lines
src/main/java/org/apache/commons/io/FileUtils.java	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##             master     #565   +/-   ##
=========================================
  Coverage     85.99%   86.00%           
+ Complexity     3498     3497    -1     
=========================================
  Files           231      231           
  Lines          8256     8251    -5     
  Branches        965      964    -1     
=========================================
- Hits           7100     7096    -4     
  Misses          865      865           
+ Partials        291      290    -1     

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