W-24226218: Deprecate TestSetupUtils instant auth helpers for removal in 15.0

[brandonpage]

Deprecates TestSetupUtils instant login helpers in 14.0 for removal in 15.0 since they are incompatible with DPoP enforcement.

[github-actions]

	Tests	Passed ✅	Skipped	Failed
SalesforceSDKCore iOS ^18 Test Results	1045 ran	1045 ✅

Test	Result
No test annotations available

[github-actions]

	Tests	Passed	Skipped	Failed ❌️
AuthFlowTester UI Test Results all	1 ran			1 ❌

Test	Result
AuthFlowTester UI Test Results all
AuthFlowTesterUITests.xctest
LegacyLoginTests.testCAOpaque_DefaultScopes_WebServerFlow()	❌ failure

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 67.83%. Comparing base (d796edb) to head (e87ba2b).

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #4176      +/-   ##
==========================================
- Coverage   71.82%   67.83%   -3.99%     
==========================================
  Files         254      254              
  Lines       23027    23027              
==========================================
- Hits        16539    15621     -918     
- Misses       6488     7406     +918     

Components	Coverage Δ
Analytics	70.78% <ø> (ø)
Common	71.20% <ø> (ø)
Core	61.72% <ø> (-5.97%)	⬇️
SmartStore	73.45% <ø> (ø)
MobileSync	88.87% <ø> (ø)
see 33 files with indirect coverage changes

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