Use consistent ITuple

This was in the incorrect namespace

Author: BillWagner

standard/patterns.md

@@ -558,7 +558,7 @@ In a *conjunctive_pattern*, the *input type* of the second pattern is narrowed b
 - If `P` is a type pattern, the *narrowed type* is the type of the type pattern's type.
 - Otherwise, if `P` is a declaration pattern, the *narrowed type* is the type of the declaration pattern's type.
 - Otherwise, if `P` is a recursive pattern that gives an explicit type, the *narrowed type* is that type.
-- Otherwise, if `P` is matched via the rules for `ITuple` in a *positional_pattern* (§11.2.5), the *narrowed type* is the type `System.Runtime.CompilerServices.ITuple`.
+- Otherwise, if `P` is matched via the rules for `ITuple` in a *positional_pattern* (§11.2.5), the *narrowed type* is the type `System.ITuple`.
 - Otherwise, if `P` is a constant pattern where the constant is not the null constant and where the expression has no *constant expression conversion* to the *input type*, the *narrowed type* is the type of the constant.
 - Otherwise, if `P` is a relational pattern where the constant expression has no *constant expression conversion* to the *input type*, the *narrowed type* is the type of the constant.
 - Otherwise, if `P` is an `or` pattern, the *narrowed type* is the common type of the *narrowed type* of the subpatterns if such a common type exists. For this purpose, the common type algorithm considers only identity, boxing, and implicit reference conversions, and it considers all subpatterns of a sequence of `or` patterns (ignoring parenthesized patterns).