[AutoDiff] Fix Optional differentiation crash.

[dan-zheng]

Fix Optional differentiation crash for non-resilient Wrapped reference type.
Add NonresilientTracked type to DifferentiationUnittest for testing.
Add and reformat tests.

Resolves SR-13377.

[dan-zheng]

cc @efremale

[dan-zheng]

@swift-ci Please test

[dan-zheng]

The Windows failure looks like an unrelated flake:

FAIL: Swift(windows-x86_64) :: Sema/struct_equatable_hashable.swift (2294 of 6726)
******************** TEST 'Swift(windows-x86_64) :: Sema/struct_equatable_hashable.swift' FAILED ********************
Script:
--
: 'RUN: at line 1';   't:\\swift\\bin\\swift-frontend.exe' -target x86_64-unknown-windows-msvc  -module-cache-path 'T:\\swift\\swift-test-results\\x86_64-unknown-windows-msvc\\clang-module-cache' -swift-version 4  -ignore-module-source-info -typo-correction-limit 10  -typecheck -verify -primary-file S:\jenkins\workspace\swift-PR-windows\swift\test\Sema\struct_equatable_hashable.swift S:\jenkins\workspace\swift-PR-windows\swift\test\Sema/Inputs/struct_equatable_hashable_other.swift -verify-ignore-unknown -swift-version 4
--
Exit Code: 1

Command Output (stdout):
--
$ ":" "RUN: at line 1"
$ "t:\\swift\\bin\\swift-frontend.exe" "-target" "x86_64-unknown-windows-msvc" "-module-cache-path" "T:\\swift\\swift-test-results\\x86_64-unknown-windows-msvc\\clang-module-cache" "-swift-version" "4" "-ignore-module-source-info" "-typo-correction-limit" "10" "-typecheck" "-verify" "-primary-file" "S:\jenkins\workspace\swift-PR-windows\swift\test\Sema\struct_equatable_hashable.swift" "S:\jenkins\workspace\swift-PR-windows\swift\test\Sema/Inputs/struct_equatable_hashable_other.swift" "-verify-ignore-unknown" "-swift-version" "4"
# command stderr:
S:\jenkins\workspace\swift-PR-windows\swift\test\Sema\struct_equatable_hashable.swift:118:126: error: incorrect message found

  if StructWithoutExplicitConformance(a: 1, b: "b") == StructWithoutExplicitConformance(a: 2, b: "a") { } // expected-error{{referencing operator function '==' on 'Equatable' requires that 'StructWithoutExplicitConformance' conform to 'Equatable'}}

                                                                                                                             ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

                                                                                                                             operator function '==' requires that 'StructWithoutExplicitConformance' conform to 'Equatable'


error: command failed with exit status: 1

Merging to unblock progress, happy to address additional feedback later.