Rename to allow all exiv2 tags as placeholders

[norbertwg]

Refers to #2238

• The syntax: the tag name has to be enclosed in colons.
• The placeholder will be replaced by translated value, not by the plain value.
• Characters in tag's translated value, which are not allowed in file names, will be replaced by underscore.

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[norbertwg]

When replacing characters, which are invalid in file names, it is currently only distinguished between Windows and others. I tried to separate Mac OS and Linux/Unix as well, but I am not sure how to do it. In XMP_environment.h I found a line of code, but it was commented with /* Todo: How to correctly recognize a Mac platform? */. The same problem I have with the test case. If somebody can give me a hint, I can refine the logic to differentiate the operating systems.

[codecov]

Codecov Report

Merging #2791 (a2b60a4) into main (fe44c8c) will increase coverage by 0.10%.
Report is 5 commits behind head on main.
The diff coverage is 90.47%.

@@            Coverage Diff             @@
##             main    #2791      +/-   ##
==========================================
+ Coverage   63.96%   64.07%   +0.10%     
==========================================
  Files         103      103              
  Lines       22344    22363      +19     
  Branches    10835    10851      +16     
==========================================
+ Hits        14293    14328      +35     
+ Misses       5828     5813      -15     
+ Partials     2223     2222       -1     

Files	Coverage Δ
app/actions.cpp	68.55% <90.47%> (+0.92%)	⬆️

... and 5 files with indirect coverage changes

[norbertwg]

This pull request is waiting for approving review since 6 months. Are there reasons not to approve this request or was it just lost out of sight?