dns: set Endpoints in resolver updates

[arjan-bal]

Presently, the DNS resolver relies on the resolver_wrapper to convert addresses to endpoints and populate the ResolverState.Endpoints field. However, when resolving Logical DNS cluster hostnames in xDS, the DNS resolver is used without the resolver_wrapper. Since the dual-stack changes have been merged, we plan to clean up code that uses the Addresses field and instead rely on the Endpoints field always being set. To support this, the DNS resolver must now handle the conversion of addresses to endpoints internally.

This change also fixes a bug in the dependency manager where it doesn't read the endpoints if the resolver provides endpoints directly instead of giving addresses.

RELEASE NOTES: N/A

[codecov]

Codecov Report

❌ Patch coverage is 91.66667% with 1 line in your changes missing coverage. Please review.
✅ Project coverage is 83.36%. Comparing base (900ffa9) to head (cd79de4).
⚠️ Report is 17 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/xds/xdsdepmgr/xds_dependency_manager.go	50.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8812      +/-   ##
==========================================
+ Coverage   83.25%   83.36%   +0.10%     
==========================================
  Files         417      417              
  Lines       32978    32928      -50     
==========================================
- Hits        27457    27450       -7     
+ Misses       4106     4085      -21     
+ Partials     1415     1393      -22     

Files with missing lines	Coverage Δ
internal/resolver/dns/dns_resolver.go	90.27% <100.00%> (+0.37%)	⬆️
internal/xds/xdsdepmgr/xds_dependency_manager.go	80.18% <50.00%> (-1.16%)	⬇️

... and 27 files with indirect coverage changes

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[eshitachandwani]

The TestRouteConfigResource failing test is due to the point 2 mentioned in this PR :
#8805
The PR also fixes it.