Restore @available annotations for iOS 14 and tvOS 14 on HKDF functions

Co-authored-by: jkoritzinsky <1571408+jkoritzinsky@users.noreply.github.com>

Author: Copilot

src/native/libs/System.Security.Cryptography.Native.Apple/pal_swiftbindings.swift

@@ -202,6 +202,7 @@ enum HKDFError: Error {
 }
 
 @_silgen_name("AppleCryptoNative_HKDFExpand")
+@available(iOS 14, tvOS 14, *)
 public func AppleCryptoNative_HKDFExpand(
     hashAlgorithm: Int32,
     prkPtr: UnsafeMutableRawPointer,
@@ -247,6 +248,7 @@ public func AppleCryptoNative_HKDFExpand(
 }
 
 @_silgen_name("AppleCryptoNative_HKDFExtract")
+@available(iOS 14, tvOS 14, *)
 public func AppleCryptoNative_HKDFExtract(
     hashAlgorithm: Int32,
     ikmPtr: UnsafeMutableRawPointer,
@@ -293,6 +295,7 @@ public func AppleCryptoNative_HKDFExtract(
 }
 
 @_silgen_name("AppleCryptoNative_HKDFDeriveKey")
+@available(iOS 14, tvOS 14, *)
 public func AppleCryptoNative_HKDFDeriveKey(
     hashAlgorithm: Int32,
     ikmPtr: UnsafeMutableRawPointer,