resolver: Add resolver.EndpointMap.All() to iterate over keys and values

[Jille]

It's nicer than iterating over the keys and looking up their values.

RELEASE NOTES: N/A

[codecov]

Codecov Report

❌ Patch coverage is 36.36364% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.44%. Comparing base (69b542a) to head (ee493e4).
⚠️ Report is 8 commits behind head on master.

Files with missing lines	Patch %	Lines
resolver/map.go	36.36%	6 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8867      +/-   ##
==========================================
+ Coverage   82.42%   82.44%   +0.01%     
==========================================
  Files         414      414              
  Lines       32750    32766      +16     
==========================================
+ Hits        26994    27013      +19     
+ Misses       4096     4090       -6     
- Partials     1660     1663       +3     

Files with missing lines	Coverage Δ
resolver/map.go	67.64% <36.36%> (-26.61%)	⬇️

... and 22 files with indirect coverage changes

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[arjan-bal]

Hi @Jille, thanks for the contribution. In addition to being more ergonomic, the iterator approach is a nice optimization as it avoids allocating a slice for the return values.

Could you also update existing call sites of Keys() and Values() within the codebase to use the new iterator methods where it makes sense? This would help validate the new API and provide better coverage.

[arjan-bal]

Can you also add a similar test for EndpointMap?