Make BorrowingSwitch a LANGUAGE_FEATURE.

It doesn't guard any source breaks, so it doesn't need to be an UPCOMING_FEATURE.
rdar://129417451

Author: jckarter

include/swift/Basic/Features.def

@@ -198,6 +198,7 @@ SUPPRESSIBLE_LANGUAGE_FEATURE(BitwiseCopyable2, 426, "BitwiseCopyable feature")
 LANGUAGE_FEATURE(BodyMacros, 415, "Function body macros")
 LANGUAGE_FEATURE(TransferringArgsAndResults, 430, "Transferring args and results")
 SUPPRESSIBLE_LANGUAGE_FEATURE(SendingArgsAndResults, 430, "Sending arg and results")
+LANGUAGE_FEATURE(BorrowingSwitch, 432, "Noncopyable type pattern matching")
 
 // Swift 6
 UPCOMING_FEATURE(ConciseMagicFile, 274, 6)
@@ -215,7 +216,6 @@ UPCOMING_FEATURE(RegionBasedIsolation, 414, 6)
 UPCOMING_FEATURE(DynamicActorIsolation, 423, 6)
 UPCOMING_FEATURE(NonfrozenEnumExhaustivity, 192, 6)
 UPCOMING_FEATURE(GlobalActorIsolatedTypesUsability, 0434, 6)
-UPCOMING_FEATURE(BorrowingSwitch, 432, 6)
 
 // Swift 7
 UPCOMING_FEATURE(ExistentialAny, 335, 7)