Refactor REST API tests to use block-based patterns

[wmathurin]

• Remove SFNativeRestRequestListener and create SFRestAPITestResponse class
• Refactor tests to use XCTestExpectation instead of custom listeners
• Fix forceTimeoutRequest double callback bug in SFRestAPI.m
• Add SFRestAPITestDelegate helper for delegate-based API testing

[github-actions]

	1 Warning
⚠️	Big PR, try to keep changes smaller if you can.

Generated by 🚫 Danger

[github-actions]

	1 Warning
⚠️	Static Analysis found an issue with one or more files you modified. Please fix the issue(s).

Clang Static Analysis Issues

File	Type	Category	Description	Line	Col
SFRestAPI	Nullability	Memory error	nil assigned to a pointer which is expected to have non-null value	98	5

Generated by 🚫 Danger

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 63.93%. Comparing base (61e2236) to head (0beb66f).
⚠️ Report is 4 commits behind head on dev.

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #3951      +/-   ##
==========================================
- Coverage   63.98%   63.93%   -0.06%     
==========================================
  Files         252      252              
  Lines       22098    22096       -2     
==========================================
- Hits        14140    14126      -14     
- Misses       7958     7970      +12     

Components	Coverage Δ
Analytics	70.78% <ø> (ø)
Common	69.76% <ø> (ø)
Core	54.83% <ø> (-0.07%)	⬇️
SmartStore	74.59% <ø> (ø)
MobileSync	87.41% <ø> (-0.12%)	⬇️

Files with missing lines	Coverage Δ
...Core/SalesforceSDKCore/Classes/RestAPI/SFRestAPI.m	87.60% <ø> (-1.97%)	⬇️

... and 5 files with indirect coverage changes

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