[stdlib] Minor doc edits

Author: natecook1000

stdlib/public/core/StringIndexConversions.swift

@@ -16,9 +16,7 @@ extension String.Index {
   ///
   /// If the index passed as `sourcePosition` represents the start of an
   /// extended grapheme cluster---the element type of a string---then the
-  /// initializer succeeds. If the index instead represents the position of a
-  /// Unicode scalar within an extended grapheme cluster or the position of an
-  /// encoded Unicode scalar value, the result is `nil`.
+  /// initializer succeeds.
   ///
   /// The following example converts the position of the Unicode scalar `"e"`
   /// into its corresponding position in the string. The character at that
@@ -43,7 +41,7 @@ extension String.Index {
   ///     let nextScalarsIndex = cafe.unicodeScalars.index(after: scalarsIndex)
   ///     let nextStringIndex = String.Index(nextScalarsIndex, within: cafe)
   ///
-  ///     print(nextIndex)
+  ///     print(nextStringIndex)
   ///     // Prints "nil"
   ///
   /// - Parameters:

stdlib/public/core/UnsafeRawBufferPointer.swift.gyb

@@ -507,8 +507,8 @@ public struct Unsafe${Mutable}RawBufferPointer
   /// Initializes the buffer's memory with the given elements, binding the
   /// initialized memory to the elements' type.
   ///
-  /// When calling the `initialize(as:from:)` method on a buffer `b`, the
-  /// memory referenced by `b` must be uninitialized or initialized to a
+  /// When calling the `initializeMemory(as:from:)` method on a buffer `b`,
+  /// the memory referenced by `b` must be uninitialized or initialized to a
   /// trivial type, and must be properly aligned for accessing `S.Element`.
   /// The buffer must contain sufficient memory to accommodate
   /// `source.underestimatedCount`.