Fix edge cases with swiftTesting rule

[calda]

This PR fixes edge cases I noticed with the new swiftTesting rule that would cause build failures or runtime issues. For example:

• Adds @Suite(.serialized) by default to match the XCTest behavior where tests run serially by default. Existing tests may not expect to be ran concurrently. I saw issues related to this in Airbnb's test suite.
• Adds import Foundation by default, since XCTest exports Foundation (common for test cases to rely on Foundation types)
• Adds import UIKit if the file uses any UIKit symbols (common in tests for app codebases) since XCTest exports UIKit
• Fixed lots of issues where operators would cause build failures. Some examples of invalid code that we were generating before include !foo == bar, !foo is Bar, try? foo == bar, etc. (should be (!(foo == bar), !(foo is Bar), (try? foo) == bar).

With these fixes, Airbnb's unit test suite builds, runs, and passes successfully after applying the swiftTesting rule (after also manually fixing a relatively reasonable number of more minor edge cases).

[codecov]

Codecov Report

Attention: Patch coverage is 98.36066% with 2 lines in your changes missing coverage. Please review.

Project coverage is 95.51%. Comparing base (5475c1b) to head (e4b9e60).

Files with missing lines	Patch %	Lines
Sources/Rules/SwiftTesting.swift	98.21%	2 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #1968   +/-   ##
========================================
  Coverage    95.51%   95.51%           
========================================
  Files          139      139           
  Lines        25505    25590   +85     
========================================
+ Hits         24360    24442   +82     
- Misses        1145     1148    +3     

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