Break ambiguity for types conforming to both UEC and SVEC (#72800)

* Break ambiguity for types conforming to both UEC and SVEC

If an encoding container conforms to _both_ UEC and SVEC and does not
itself implement support for [U]Int128, there is an ambiguity between
the two default implementations. Add additional defaults defined on
the intersection of the protocols to resolve this.

* Update abi tests for new ambiguity breakers.

Author: stephentyrone

stdlib/public/core/Codable.swift

@@ -7102,3 +7102,29 @@ extension SingleValueDecodingContainer {
     )
   }
 }
+
+// Default implementations for types with stricter availability than SVEC & UEC
+// We need these to break ambiguity when an encoding container conforms to both.
+extension SingleValueEncodingContainer where Self: UnkeyedEncodingContainer {
+  @available(SwiftStdlib 6.0, *)
+  public mutating func encode(_ value: Int128) throws {
+    throw EncodingError.invalidValue(
+      value,
+      EncodingError.Context(
+        codingPath: codingPath,
+        debugDescription: "Encoder has not implemented support for Int128"
+      )
+    )
+  }
+  
+  @available(SwiftStdlib 6.0, *)
+  public mutating func encode(_ value: UInt128) throws {
+    throw EncodingError.invalidValue(
+      value,
+      EncodingError.Context(
+        codingPath: codingPath,
+        debugDescription: "Encoder has not implemented support for UInt128"
+      )
+    )
+  }
+}

test/abi/macOS/arm64/stdlib.swift

@@ -271,6 +271,7 @@ Added: _$ss28SingleValueDecodingContainerPsE6decodeys6Int128VAEmKF
 Added: _$ss28SingleValueEncodingContainerP6encodeyys6Int128VKFTj
 Added: _$ss28SingleValueEncodingContainerP6encodeyys6Int128VKFTq
 Added: _$ss28SingleValueEncodingContainerPsE6encodeyys6Int128VKF
+Added: _$ss28SingleValueEncodingContainerPss07UnkeyedcD0RzrlE6encodeyys6Int128VKF
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys6Int128VSgAFm_0I0QztKFTj
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys6Int128VSgAFm_0I0QztKFTq
 Added: _$ss30KeyedDecodingContainerProtocolP6decode_6forKeys6Int128VAFm_0G0QztKFTj
@@ -408,6 +409,7 @@ Added: _$ss28SingleValueDecodingContainerPsE6decodeys7UInt128VAEmKF
 Added: _$ss28SingleValueEncodingContainerP6encodeyys7UInt128VKFTj
 Added: _$ss28SingleValueEncodingContainerP6encodeyys7UInt128VKFTq
 Added: _$ss28SingleValueEncodingContainerPsE6encodeyys7UInt128VKF
+Added: _$ss28SingleValueEncodingContainerPss07UnkeyedcD0RzrlE6encodeyys7UInt128VKF
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys7UInt128VSgAFm_0I0QztKFTj
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys7UInt128VSgAFm_0I0QztKFTq
 Added: _$ss30KeyedDecodingContainerProtocolP6decode_6forKeys7UInt128VAFm_0G0QztKFTj

test/abi/macOS/x86_64/stdlib.swift

@@ -271,6 +271,7 @@ Added: _$ss28SingleValueDecodingContainerPsE6decodeys6Int128VAEmKF
 Added: _$ss28SingleValueEncodingContainerP6encodeyys6Int128VKFTj
 Added: _$ss28SingleValueEncodingContainerP6encodeyys6Int128VKFTq
 Added: _$ss28SingleValueEncodingContainerPsE6encodeyys6Int128VKF
+Added: _$ss28SingleValueEncodingContainerPss07UnkeyedcD0RzrlE6encodeyys6Int128VKF
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys6Int128VSgAFm_0I0QztKFTj
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys6Int128VSgAFm_0I0QztKFTq
 Added: _$ss30KeyedDecodingContainerProtocolP6decode_6forKeys6Int128VAFm_0G0QztKFTj
@@ -408,6 +409,7 @@ Added: _$ss28SingleValueDecodingContainerPsE6decodeys7UInt128VAEmKF
 Added: _$ss28SingleValueEncodingContainerP6encodeyys7UInt128VKFTj
 Added: _$ss28SingleValueEncodingContainerP6encodeyys7UInt128VKFTq
 Added: _$ss28SingleValueEncodingContainerPsE6encodeyys7UInt128VKF
+Added: _$ss28SingleValueEncodingContainerPss07UnkeyedcD0RzrlE6encodeyys7UInt128VKF
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys7UInt128VSgAFm_0I0QztKFTj
 Added: _$ss30KeyedDecodingContainerProtocolP15decodeIfPresent_6forKeys7UInt128VSgAFm_0I0QztKFTq
 Added: _$ss30KeyedDecodingContainerProtocolP6decode_6forKeys7UInt128VAFm_0G0QztKFTj