On type mismatch caused by assignment, point at assignee

* Do not emit unnecessary E0308 after E0070
* Show fewer errors on `while let` missing `let`
* Hide redundant E0308 on `while let` missing `let`
* Point at binding definition when possible on invalid assignment
* do not point at closure twice
* do not suggest `if let` for literals in lhs
* account for parameter types

src/test/ui/integral-variable-unification-error.rs

@@ -1,6 +1,8 @@
 fn main() {
-    let mut x = 2;
+    let mut x //~ NOTE expected due to the type of this binding
+        =
+        2; //~ NOTE expected due to this value
     x = 5.0;
     //~^ ERROR mismatched types
-    //~| expected integer, found floating-point number
+    //~| NOTE expected integer, found floating-point number
 }