Cherry-pick #6804 and dependencies to v1.60.x release branch

[dfawley]

(Relnotes will need to be manually added.)

RELEASE NOTES:

• client: remove deprecated WithServiceConfig DialOption
• client: fix race that could cause a deadlock while entering idle mode and receiving a name resolver update

[codecov]

Codecov Report

Merging #6838 (4357bac) into v1.60.x (dd39cdb) will increase coverage by 0.13%.
The diff coverage is 88.71%.

Additional details and impacted files

@@             Coverage Diff             @@
##           v1.60.x    #6838      +/-   ##
===========================================
+ Coverage    83.44%   83.57%   +0.13%     
===========================================
  Files          285      285              
  Lines        30961    30776     -185     
===========================================
- Hits         25836    25722     -114     
+ Misses        4048     3995      -53     
+ Partials      1077     1059      -18     

Files	Coverage Δ
dialoptions.go	88.84% <100.00%> (-0.10%)	⬇️
internal/buffer/unbounded.go	100.00% <100.00%> (ø)
internal/channelz/funcs.go	95.02% <100.00%> (+0.04%)	⬆️
internal/grpcsync/callback_serializer.go	100.00% <100.00%> (+6.25%)	⬆️
picker_wrapper.go	88.88% <50.00%> (-1.81%)	⬇️
internal/idle/idle.go	88.40% <92.45%> (+26.18%)	⬆️
balancer_wrapper.go	82.92% <87.95%> (ø)
clientconn.go	91.18% <88.07%> (-0.25%)	⬇️
resolver_wrapper.go	85.04% <85.04%> (ø)

... and 18 files with indirect coverage changes