[stdlib] improve silgen names and better document intention

Author: glessard

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -730,9 +730,9 @@ extension Unsafe${Mutable}BufferPointer {
   @_alwaysEmitIntoClient
   // This custom silgen name is chosen to not interfere with the old ABI
 % if Mutable:
-  @_silgen_name("$_swift_se0333_UnsafeMutableBufferPointer_withMemoryRebound")
+  @_silgen_name("_swift_se0333_UnsafeMutableBufferPointer_withMemoryRebound")
 % else:
-  @_silgen_name("$_swift_se0333_UnsafeBufferPointer_withMemoryRebound")
+  @_silgen_name("_swift_se0333_UnsafeBufferPointer_withMemoryRebound")
 % end
   public func withMemoryRebound<T, Result>(
     to type: T.Type,

stdlib/public/core/UnsafePointer.swift

@@ -1013,7 +1013,7 @@ public struct UnsafeMutablePointer<Pointee>: _Pointer {
   @inlinable
   @_alwaysEmitIntoClient
   // This custom silgen name is chosen to not interfere with the old ABI
-  @_silgen_name("$_swift_se0333_UnsafeMutablePointer_withMemoryRebound")
+  @_silgen_name("_swift_se0333_UnsafeMutablePointer_withMemoryRebound")
   public func withMemoryRebound<T, Result>(
     to type: T.Type,
     capacity count: Int,

stdlib/public/core/UnsafeRawBufferPointer.swift.gyb

@@ -465,6 +465,7 @@ extension Unsafe${Mutable}RawBufferPointer {
   ///     with `type`.
   @inlinable
   @_alwaysEmitIntoClient
+  // This custom silgen name is chosen to not interfere with the old ABI
   @_silgen_name("_swift_se0349_UnsafeMutableRawBufferPointer_storeBytes")
   public func storeBytes<T>(
     of value: T, toByteOffset offset: Int = 0, as type: T.Type

stdlib/public/core/UnsafeRawPointer.swift

@@ -1226,6 +1226,7 @@ public struct UnsafeMutableRawPointer: _Pointer {
   ///   - type: The type of `value`.
   @inlinable
   @_alwaysEmitIntoClient
+  // This custom silgen name is chosen to not interfere with the old ABI
   @_silgen_name("_swift_se0349_UnsafeMutableRawPointer_storeBytes")
   public func storeBytes<T>(
     of value: T, toByteOffset offset: Int = 0, as type: T.Type