cherry-pick #8215, #8302 and #8304 to v1.71.x branch

[eshitachandwani]

Fixes: #8207
Original PR: #8215 , #8302 , #8304

RELEASE NOTES:

• resolver/delegatingresolver: Proxy connections are no longer attempted for targets with non-TCP network types.

[codecov]

Codecov Report

Attention: Patch coverage is 90.32258% with 6 lines in your changes missing coverage. Please review.

Project coverage is 82.45%. Comparing base (574c0a5) to head (39ed115).
Report is 1 commits behind head on v1.71.x.

Files with missing lines	Patch %	Lines
.../resolver/delegatingresolver/delegatingresolver.go	90.00%	4 Missing and 2 partials ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##           v1.71.x    #8298      +/-   ##
===========================================
+ Coverage    82.19%   82.45%   +0.25%     
===========================================
  Files          387      387              
  Lines        38959    38986      +27     
===========================================
+ Hits         32023    32146     +123     
+ Misses        5618     5539      -79     
+ Partials      1318     1301      -17     

Files with missing lines	Coverage Δ
internal/transport/http2_client.go	91.47% <100.00%> (ø)
internal/transport/http_util.go	92.06% <100.00%> (ø)
.../resolver/delegatingresolver/delegatingresolver.go	85.50% <90.00%> (+3.28%)	⬆️

... and 23 files with indirect coverage changes

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