Add test for doc_comment_code_block_small_heuristics

This test is based on the `use_small_heuristics` tests. It tests that
the code *outside* the doc comment gets formatted using `Max`, while the
code inside doc comments gets formatted using `Default`.

Author: joshtriplett

tests/source/configs/doc_comment_code_block_small_heuristics/max-to-default.rs

@@ -0,0 +1,68 @@
+// rustfmt-format_code_in_doc_comments: true
+// rustfmt-use_small_heuristics: Max
+// rustfmt-doc_comment_code_block_small_heuristics: Default
+
+/// Start of a doc comment.
+///
+/// ```
+/// enum Lorem {
+///     Ipsum,
+///     Dolor(bool),
+///     Sit { amet: Consectetur, adipiscing: Elit },
+/// }
+///
+/// fn main() {
+///     lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing");
+///
+///     let lorem = Lorem { ipsum: dolor, sit: amet };
+///
+///     let lorem = if ipsum { dolor } else { sit };
+/// }
+///
+/// fn format_let_else() {
+///     let Some(a) = opt else {};
+///
+///     let Some(b) = opt else { return };
+///
+///     let Some(c) = opt else { return };
+///
+///     let Some(d) = some_very_very_very_very_long_name else { return };
+/// }
+/// ```
+///
+/// End of a doc comment.
+struct S;
+
+enum Lorem {
+    Ipsum,
+    Dolor(bool),
+    Sit {
+        amet: Consectetur,
+        adipiscing: Elit,
+    },
+}
+
+fn main() {
+    lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing");
+
+    let lorem = Lorem {
+        ipsum: dolor,
+        sit: amet,
+    };
+
+    let lorem = if ipsum {
+        dolor
+    } else {
+        sit
+    };
+}
+
+fn format_let_else() {
+    let Some(a) = opt else {};
+
+    let Some(b) = opt else { return };
+
+    let Some(c) = opt else { return };
+
+    let Some(d) = some_very_very_very_very_long_name else { return };
+}

tests/target/configs/doc_comment_code_block_small_heuristics/max-to-default.rs

@@ -0,0 +1,71 @@
+// rustfmt-format_code_in_doc_comments: true
+// rustfmt-use_small_heuristics: Max
+// rustfmt-doc_comment_code_block_small_heuristics: Default
+
+/// Start of a doc comment.
+///
+/// ```
+/// enum Lorem {
+///     Ipsum,
+///     Dolor(bool),
+///     Sit { amet: Consectetur, adipiscing: Elit },
+/// }
+///
+/// fn main() {
+///     lorem(
+///         "lorem",
+///         "ipsum",
+///         "dolor",
+///         "sit",
+///         "amet",
+///         "consectetur",
+///         "adipiscing",
+///     );
+///
+///     let lorem = Lorem {
+///         ipsum: dolor,
+///         sit: amet,
+///     };
+///
+///     let lorem = if ipsum { dolor } else { sit };
+/// }
+///
+/// fn format_let_else() {
+///     let Some(a) = opt else {};
+///
+///     let Some(b) = opt else { return };
+///
+///     let Some(c) = opt else { return };
+///
+///     let Some(d) = some_very_very_very_very_long_name else {
+///         return;
+///     };
+/// }
+/// ```
+///
+/// End of a doc comment.
+struct S;
+
+enum Lorem {
+    Ipsum,
+    Dolor(bool),
+    Sit { amet: Consectetur, adipiscing: Elit },
+}
+
+fn main() {
+    lorem("lorem", "ipsum", "dolor", "sit", "amet", "consectetur", "adipiscing");
+
+    let lorem = Lorem { ipsum: dolor, sit: amet };
+
+    let lorem = if ipsum { dolor } else { sit };
+}
+
+fn format_let_else() {
+    let Some(a) = opt else {};
+
+    let Some(b) = opt else { return };
+
+    let Some(c) = opt else { return };
+
+    let Some(d) = some_very_very_very_very_long_name else { return };
+}