Provide more context when mutably borrowing an imutably borrowed value

[estebank]

Point at statics and consts being mutable borrowed or written to:

error[E0594]: cannot assign to immutable static item `NUM`
  --> $DIR/E0594.rs:4:5
   |
LL | static NUM: i32 = 18;
   | --------------- this `static` cannot be written to
...
LL |     NUM = 20;
   |     ^^^^^^^^ cannot assign

Point at the expression that couldn't be mutably borrowed from a pattern:

error[E0596]: cannot borrow data in a `&` reference as mutable
  --> $DIR/mut-pattern-of-immutable-borrow.rs:19:14
   |
LL |     match &arg.field {
   |           ---------- this cannot be borrowed as mutable
LL |         Some(ref mut s) => s.push('a'),
   |              ^^^^^^^^^ cannot borrow as mutable

Partially address #74617.

[rustbot]

This PR modifies tests/ui/issues/. If this PR is adding new tests to tests/ui/issues/,
please refrain from doing so, and instead add it to more descriptive subdirectories.

[rustbot]

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