Conform Identifier to Sendable and Hashable

This isn't explicitly needed for this problem but it seems as though
the default for all types that can conform to Sendable/Hashable should

This also sets up this new type for Swift 6.0 (and the current Swift 5.10)
to pass this type around safely when needed

As well as allows Identifier to be a key in a dictionary which could be
a common scenario

Sources/SwiftSyntax/Identifier.swift

@@ -11,7 +11,7 @@
 //===----------------------------------------------------------------------===//
 
 /// An abstraction for sanitized values on a token.
-public struct Identifier: Equatable {
+public struct Identifier: Equatable, Hashable, Sendable {
   /// The sanitized `text` of a token.
   public let name: String