[Tests] Add static keypaths tests.

Author: amritpan

build.sh

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+MODE=$1
+TEST=$2
+
+pushd ../build/${MODE}/swift-macosx-arm64
+xcrun ninja -j 8 swift-frontend
+#xcrun ninja -j 8 swift-refactor
+#xcrun ninja swift-demangle
+#xcrun ninja swift-serialize-diagnostics
+#xcrun ninja sil-opt
+#xcrun ninja swift-ide-test
+#xcrun ninja sourcekitd-test
+#xcrun ninja stdlib
+#xcrun ninja swift-remoteast
+popd
+python3 ../llvm-project/llvm/utils/lit/lit.py -sv --param swift_site_config=../build/${MODE}/swift-macosx-arm64/test-macosx-x86_64/lit.site.cfg ${TEST}

test/ModuleInterface/static_keypaths.swift

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+// RUN: %empty-directory(%t/src)
+// RUN: split-file %s %t/src
+
+/// Build LibA
+// RUN: %host-build-swift %t/src/LibA.swift -swift-version 5 -emit-module -emit-library -enable-library-evolution -module-name LibA -o %t/%target-library-name(LibA) -emit-module-interface-path %t/LibA.swiftinterface
+
+// Build LibB
+// RUN: %target-build-swift %t/src/LibB.swift -I %t -L %t -l LibA -swift-version 5 -emit-module -emit-library -module-name LibB -o %t/%target-library-name(LibB)
+
+// Build LibC
+// RUN: %target-build-swift %t/src/LibC.swift -I %t -L %t -l LibA -swift-version 5 -emit-module -emit-library -module-name LibC -o %t/%target-library-name(LibC)
+
+// Build & run main.swift
+// RUN: %target-build-swift -I %t -L %t -l LibA -l LibB -l LibC %t/src/main.swift -o %t/a.out
+// RUN: %target-codesign %t/%target-library-name(LibA)
+// RUN: %target-codesign %t/%target-library-name(LibB)
+// RUN: %target-codesign %t/%target-library-name(LibC)
+// RUN: %target-codesign %t/a.out
+// RUN: %target-run %t/a.out | %FileCheck %s
+
+// REQUIRES: executable_test
+// REQUIRES: OS=macosx
+
+//--- LibA.swift
+public struct AStruct {
+  public static var property1: Int = 1
+  public static var property2: Int = 2
+  private(set) public static var property3: Int = 1
+  private(set) public static var property4: Int = 4
+}
+
+//--- LibB.swift
+import LibA
+
+public let keyPath1FromLibB = \AStruct.Type.property1
+public let keyPath2FromLibB = \AStruct.Type.property2
+public let keyPath3FromLibB = \AStruct.Type.property3
+public let keyPath4FromLibB = \AStruct.Type.property4
+public var keyPath5FromLibB = \AStruct.Type.property1 // WritableKeyPath with public setter
+
+//--- LibC.swift
+import LibA
+
+public let keyPath1FromLibC = \AStruct.Type.property1
+public let keyPath2FromLibC = \AStruct.Type.property2
+public let keyPath3FromLibC = \AStruct.Type.property3 // Read-only with private setter
+public let keyPath4FromLibC = \AStruct.Type.property4
+
+//--- main.swift
+import LibB
+import LibC
+
+// CHECK: true
+print(keyPath1FromLibB == keyPath1FromLibC)
+// CHECK: true
+print(keyPath1FromLibB != keyPath2FromLibC)
+
+// CHECK: true
+print(keyPath3FromLibB == keyPath3FromLibC)
+// CHECK: true
+print(keyPath3FromLibB != keyPath4FromLibC)
+
+// CHECK: false
+print(keyPath5FromLibB == keyPath3FromLibC)