[stdlib] Generalize Unsafe[Mutable]BufferPointer.indices

Author: lorentey

stdlib/public/core/UnsafeBufferPointer.swift.gyb

@@ -255,6 +255,13 @@ extension Unsafe${Mutable}BufferPointer where Element: ~Copyable {
   @safe
   public var endIndex: Int { count }
 
+  @inlinable
+  @_preInverseGenerics
+  public var indices: Range<Int> {
+    // Not checked because init forbids negative count.
+    unsafe Range(uncheckedBounds: (0, count))
+  }
+
   @inlinable
   @_preInverseGenerics
   public func index(after i: Int) -> Int {
@@ -684,13 +691,6 @@ extension Unsafe${Mutable}BufferPointer:
     _debugPrecondition(range.upperBound <= bounds.upperBound)
   }
 
-  @inlinable // unsafe-performance
-  @safe
-  public var indices: Indices {
-    // Not checked because init forbids negative count.
-    return unsafe Indices(uncheckedBounds: (startIndex, endIndex))
-  }
-
   /// Accesses a contiguous subrange of the buffer's elements.
   ///
   /// The accessed slice uses the same indices for the same elements as the