Update stdlib on_unimplemented attributes and doctests using String to the new path.

Also reverts some UI test changes that were due to on_unimplemented path being wrong.

Author: zachs18

library/core/src/any.rs

@@ -709,7 +709,7 @@ impl fmt::Debug for TypeId {
 /// ```rust
 /// assert_eq!(
 ///     std::any::type_name::<Option<String>>(),
-///     "core::option::Option<alloc::string::String>",
+///     "core::option::Option<alloc::string::string::String>",
 /// );
 /// ```
 #[must_use]

library/core/src/convert/mod.rs

@@ -575,7 +575,7 @@ pub trait Into<T>: Sized {
 #[rustc_diagnostic_item = "From"]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[rustc_on_unimplemented(on(
-    all(_Self = "&str", T = "alloc::string::String"),
+    all(_Self = "&str", T = "alloc::string::string::String"),
     note = "to coerce a `{T}` into a `{Self}`, use `&*` as a prefix",
 ))]
 #[doc(search_unbox)]

library/core/src/iter/traits/collect.rs

@@ -264,7 +264,7 @@ pub trait FromIterator<A>: Sized {
         label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
     ),
     on(
-        _Self = "alloc::string::String",
+        _Self = "alloc::string::string::String",
         label = "`{Self}` is not an iterator; try calling `.chars()` or `.bytes()`"
     ),
     on(

library/core/src/ops/index.rs

@@ -153,7 +153,7 @@ see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#ind
 see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
     ),
     on(
-        _Self = "alloc::string::String",
+        _Self = "alloc::string::string::String",
         note = "you can use `.chars().nth()` or `.bytes().nth()`
 see chapter in The Book <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"
     ),

library/core/src/slice/index.rs

@@ -161,7 +161,7 @@ mod private_slice_index {
 #[rustc_on_unimplemented(
     on(T = "str", label = "string indices are ranges of `usize`",),
     on(
-        all(any(T = "str", T = "&str", T = "alloc::string::String"), _Self = "{integer}"),
+        all(any(T = "str", T = "&str", T = "alloc::string::string::String"), _Self = "{integer}"),
         note = "you can use `.chars().nth()` or `.bytes().nth()`\n\
                 for more information, see chapter 8 in The Book: \
                 <https://doc.rust-lang.org/book/ch08-02-strings.html#indexing-into-strings>"