fix: Handle Depth header for COPY as this is required by RFC

[susnux]

Currently Sabre\DAV does not support the Depth header on COPY and MOVE.
But the RFC4918 requires servers to do so, the header is not required but:

• If the header is missing 'infinity' shall be assumed -> This is how we handle every request currently
• For MOVE the header, if available, must be 'infinity' -> We just have to check the header and throw bad request otherwise
• For COPY the header may 'infinity' or a positive integer including 0
  • The depths defines how many levels of children shall be copied
  • If the depth is zero only the collection and its properties are copied, but not any children

So especially the COPY method is currently broken, we noticed this when using the WebDAV litmus test bench (version 0.14) which checks for shallow copies (meaning copy a collection with depth 0).

This PR fixes all of this points, while trying to keep backwards compatible. Of cause any using application that implements ICopyTarget::copyInto is still broken and need to adapt to the depth change (it continues to work as before, but the bug fix does not propagate).

Reference from the RFC:

• The requirement on the server support of COPY Depth 'infinity' and '0': rfc4918#section-9.8.3
• For MOVE only Depth: infinity is allowed: rfc4918#section-9.9.2

[susnux]

ping again, also cc @phil-davis

Would be great to get this fixed so sabre passes the litmus test v15 ( https://github.com/notroj/litmus previously http://www.webdav.org/neon/litmus/ )

[susnux]

Anything I can help with to get this reviewed? (I do not want to bug you but this would be a great to get fixed :) ).

[DeepDiver1975]

I miss the ci status - what's going on here?

[DeepDiver1975]

I miss the ci status - what's going on here?

@susnux can I ask you to rebase this pull request ... THX

[susnux]

can I ask you to rebase this pull request ... THX

@DeepDiver1975 sure, done!

Noticed I had some code style issues / compatibility issues because I was using PHP 8+ syntax and tests use PHP 7.4. This is now fixed.

[codecov]

Codecov Report

Attention: Patch coverage is 96.42857% with 1 line in your changes missing coverage. Please review.

Project coverage is 97.24%. Comparing base (ed901a9) to head (1af1212).
Report is 9 commits behind head on master.

Files with missing lines	Patch %	Lines
lib/DAV/Tree.php	93.33%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##             master    #1495      +/-   ##
============================================
+ Coverage     97.23%   97.24%   +0.01%     
- Complexity     2836     2842       +6     
============================================
  Files           175      175              
  Lines          9028     9040      +12     
============================================
+ Hits           8778     8791      +13     
+ Misses          250      249       -1     

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[susnux]

Noticed it is still open, is there anything I can help with?

[kesselb]

cc @susnux can you rebase, to have a recent ci run?

[susnux]

can you rebase, to have a recent ci run?

Sure, done

[susnux]

@kesselb I pushed a commit solving your comments

[susnux]

@phil-davis anything else to do, to get this PR merged?