xds: change clusterimpl LB policy to use updates from dependency manager

[eshitachandwani]

This PR removes unnecessary fields from clusterimpl LBConfig and instead used the XDSConfig from the dependency manager for it.

This PR currently also has the changes of #8777.
Only the last commit (e320853) has the changes relevant to this PR. Changes will be much smaller once the earlier PR is merged.

RELEASE NOTES: None

[codecov]

Codecov Report

❌ Patch coverage is 77.21088% with 67 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.38%. Comparing base (4046676) to head (e320853).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
internal/xds/balancer/cdsbalancer/cdsbalancer.go	65.13%	36 Missing and 17 partials ⚠️
internal/xds/balancer/clusterimpl/clusterimpl.go	83.72%	3 Missing and 4 partials ⚠️
internal/xds/xdsdepmgr/xds_dependency_manager.go	90.00%	4 Missing and 1 partial ⚠️
internal/xds/balancer/cdsbalancer/configbuilder.go	92.30%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8799      +/-   ##
==========================================
- Coverage   83.42%   83.38%   -0.04%     
==========================================
  Files         418      411       -7     
  Lines       32897    32532     -365     
==========================================
- Hits        27443    27126     -317     
+ Misses       4069     4041      -28     
+ Partials     1385     1365      -20     

Files with missing lines	Coverage Δ
balancer/pickfirst/pickfirst.go	89.62% <100.00%> (+0.50%)	⬆️
...ds/balancer/cdsbalancer/configbuilder_childname.go	100.00% <ø> (ø)
internal/xds/balancer/clusterimpl/config.go	100.00% <ø> (ø)
internal/xds/clusterspecifier/rls/rls.go	62.50% <100.00%> (ø)
internal/xds/resolver/serviceconfig.go	86.04% <100.00%> (-2.02%)	⬇️
internal/xds/resolver/xds_resolver.go	86.95% <100.00%> (-1.81%)	⬇️
internal/xds/balancer/cdsbalancer/configbuilder.go	92.42% <92.30%> (ø)
internal/xds/xdsdepmgr/xds_dependency_manager.go	88.72% <90.00%> (+7.84%)	⬆️
internal/xds/balancer/clusterimpl/clusterimpl.go	82.32% <83.72%> (-1.40%)	⬇️
internal/xds/balancer/cdsbalancer/cdsbalancer.go	72.36% <65.13%> (-12.97%)	⬇️

... and 33 files with indirect coverage changes

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