Rename RefTokenTreeCursor.

Because `TokenStreamIter` is a much better name for a `TokenStream`
iterator. Also rename the `TokenStream::trees` method as
`TokenStream::iter`, and some local variables.

compiler/rustc_expand/src/proc_macro_server.rs

@@ -112,9 +112,9 @@ impl FromInternal<(TokenStream, &mut Rustc<'_, '_>)> for Vec<TokenTree<TokenStre
         // Estimate the capacity as `stream.len()` rounded up to the next power
         // of two to limit the number of required reallocations.
         let mut trees = Vec::with_capacity(stream.len().next_power_of_two());
-        let mut cursor = stream.trees();
+        let mut iter = stream.iter();
 
-        while let Some(tree) = cursor.next() {
+        while let Some(tree) = iter.next() {
             let (Token { kind, span }, joint) = match tree.clone() {
                 tokenstream::TokenTree::Delimited(span, _, delim, tts) => {
                     let delimiter = pm::Delimiter::from_internal(delim);