issues with _UID generation

[BertKoor]

fix: #4828, #5261

Generation of a new _UID when mandatory is the responsibility of GedcomImportService, and should not be done elsewhere.

PafUid->canonical() should NOT generate a value, even when absent. This was causing it getting a value even when none was required, possibly even CHANGING existing values which should never occur.

Changed _UID tag to hidden for OBJE, REPO & SOUR, can be put on the form with button "Edit with all GEDCOM tags" when needed.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 35.20%. Comparing base (2b3a3e6) to head (ddc1b8a).
⚠️ Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
app/Gedcom.php	0.00%	3 Missing ⚠️
app/Elements/PafUid.php	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #5293   +/-   ##
=========================================
  Coverage     35.20%   35.20%           
  Complexity    11236    11236           
=========================================
  Files          1159     1159           
  Lines         48108    48108           
=========================================
  Hits          16937    16937           
  Misses        31171    31171           

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