[stdlib] Update platform versions for SwiftStdlib 5.6; define placeholders for SwiftStdlib 5.7

[lorentey]

Set platform version numbers for SwiftStdlib 5.6 to match the SDK releases that shipped with Xcode 13.3 beta 1.

Define the SwiftStdlib 5.7 macro with placeholder version numbers, and update APIs that are currently scheduled to ship from the main branch to use this instead of the generic SwiftStdlib 9999.

rdar://88154764

[lorentey]

@swift-ci test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - 61268aa

[lorentey]

--- /Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/swift/test/api-digester/Outputs/cake.json	2022-01-27 14:45:11.000000000 -0800
+++ /Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/buildbot_incremental/swift-macosx-x86_64/test-macosx-x86_64/api-digester/Output/dump-module.swift.tmp.dump.json	2022-01-27 16:59:22.000000000 -0800
@@ -1713,8 +1713,7 @@
           "name": "CodingKeyRepresentable",
           "printedName": "CodingKeyRepresentable",
           "usr": "s:s22CodingKeyRepresentableP",
-          "mangledName": "$ss22CodingKeyRepresentableP",
-          "isABIPlaceholder": true
+          "mangledName": "$ss22CodingKeyRepresentableP"
         },
         {
           "kind": "Conformance",

--

This may be a related failure.

[lorentey]

/Users/buildnode/jenkins/workspace/swift-PR-macos/branch-main/swift/test/Sanitizers/tsan/racy_async_let_fibonacci.swift:70:11: error: CHECK: expected string not found in input
// CHECK: ThreadSanitizer: Swift access race
          ^

This is definitely unrelated.

[lorentey]

@swift-ci test

[swift-ci]

Build failed
Swift Test OS X Platform
Git Sha - d94ed862902855d626d78ce3a6eaaf1681657364

[benrimmington]

You may need to update cake.json and cake-abi.json as well.

[lorentey]

@swift-ci test