Add rule to avoid prefixing Swift Testing test case methods with "test"

[calda]

Summary

This PR proposes a new rule to avoid prefixing Swift Testing test case methods with a "test" prefix. Autocorrect is implemented in the swiftTestingTestCaseNames SwiftFormat rule (nicklockwood/SwiftFormat#1979).

import Testing

/// WRONG
struct SpaceshipTests {
  @Test
  func testWarpDriveEnablesFTLTravel() { ... }

  @Test
  func testArtificialGravityMatchesEarthGravity() { ... }
}

/// RIGHT
struct SpaceshipTests {
  @Test
  func warpDriveEnablesFTLTravel() { ... }

  @Test
  func artificialGravityMatchesEarthGravity() { ... }
}

Reasoning

Prefixing test case methods with "test" was necessary with XCTest, but is not necessary in Swift Testing. Idiomatic usage of Swift Testing excludes the "test" prefix.

From Apple's migration guide:

[miguel-jimenez-0529]

Nice!

[miguel-jimenez-0529]

Thanks!