[stdlib] ManagedBuffer: Fix misapplied linkage names for legacy entry points

I accidentally copy and pasted the mangled symbol names in the wrong order, so existing callers got directed to the wrong entry points, and things got terribly, terribly wrong.

(We badly need a sensible replacement for these `@_silgen_name` hacks.)

Huge thanks to @edymtt for spotting this!

rdar://127016847

Author: lorentey

stdlib/public/core/ManagedBuffer.swift

@@ -170,7 +170,7 @@ extension ManagedBuffer where Element: ~Copyable {
 
 extension ManagedBuffer {
   @_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
-  @_silgen_name("$ss13ManagedBufferC25withUnsafeMutablePointersyqd__qd__SpyxG_Spyq_GtKXEKlF")
+  @_silgen_name("$ss13ManagedBufferC32withUnsafeMutablePointerToHeaderyqd__qd__SpyxGKXEKlF")
   @usableFromInline
   internal final func __legacy_withUnsafeMutablePointerToHeader<R>(
     _ body: (UnsafeMutablePointer<Header>) throws -> R
@@ -179,7 +179,7 @@ extension ManagedBuffer {
   }
 
   @_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
-  @_silgen_name("$ss13ManagedBufferC32withUnsafeMutablePointerToHeaderyqd__qd__SpyxGKXEKlF")
+  @_silgen_name("$ss13ManagedBufferC34withUnsafeMutablePointerToElementsyqd__qd__Spyq_GKXEKlF")
   @usableFromInline
   internal final func __legacy_withUnsafeMutablePointerToElements<R>(
     _ body: (UnsafeMutablePointer<Element>) throws -> R
@@ -188,7 +188,7 @@ extension ManagedBuffer {
   }
 
   @_spi(SwiftStdlibLegacyABI) @available(swift, obsoleted: 1)
-  @_silgen_name("$ss13ManagedBufferC34withUnsafeMutablePointerToElementsyqd__qd__Spyq_GKXEKlF")
+  @_silgen_name("$ss13ManagedBufferC25withUnsafeMutablePointersyqd__qd__SpyxG_Spyq_GtKXEKlF")
   @usableFromInline
   internal final func __legacy_withUnsafeMutablePointers<R>(
     _ body: (