Add UI test for primitive_method_to_numeric_cast

tests/ui/primitive_method_to_numeric_cast.fixed

@@ -0,0 +1,5 @@
+#![warn(clippy::primitive_method_to_numeric_cast)]
+
+fn main() {
+    let _ = u16::MAX as usize; //~ primitive_method_to_numeric_cast
+}

tests/ui/primitive_method_to_numeric_cast.rs

@@ -0,0 +1,5 @@
+#![warn(clippy::primitive_method_to_numeric_cast)]
+
+fn main() {
+    let _ = u16::max as usize; //~ primitive_method_to_numeric_cast
+}

tests/ui/primitive_method_to_numeric_cast.stderr

@@ -0,0 +1,15 @@
+error: casting function pointer `u16::max` to `usize`
+  --> tests/ui/primitive_method_to_numeric_cast.rs:4:13
+   |
+LL |     let _ = u16::max as usize;
+   |             ^^^^^^^^^^^^^^^^^
+   |
+   = note: `-D clippy::primitive-method-to-numeric-cast` implied by `-D warnings`
+   = help: to override `-D warnings` add `#[allow(clippy::primitive_method_to_numeric_cast)]`
+help: did you mean to use the associated constant?
+   |
+LL |     let _ = u16::MAX as usize;
+   |             ~~~~~~~~~~~~~~~~~
+
+error: aborting due to 1 previous error
+