Account for match arms statements without a block

[estebank]

Given the following code:

    match S::get(1) {
        Some(Val::Foo) => ();
        _ => (),
    }

The current output is:

error: expected one of `,`, `.`, `?`, `}`, or an operator, found `;`
  --> src/main.rs:26:29
   |
26 |         Some(Val::Foo) => ();
   |                        --   ^ expected one of `,`, `.`, `?`, `}`, or an operator
   |                        |
   |                        while parsing the `match` arm starting here

error[E0283]: type annotations needed
  --> src/main.rs:25:11
   |
4  |     fn get<K, V: Default>(_: K) -> Option<V> {
   |                  ------- required by this bound in `S::get`
...
25 |     match S::get(1) {
   |           ^^^^^^ cannot infer type for type parameter `V` declared on the associated function `get`
   |
   = note: cannot satisfy `_: Default`
help: consider specifying the type arguments in the function call
   |
25 |     match S::get::<K, V>(1) {
   |                 ^^^^^^^^

The first error is a generic parse error that we could account for. The second is an inference error that would be completely solved if the parse error was recovered more gracefully.

Ideally, for a generic case the output should look like:

error: expected one of `,`, `.`, `?`, `}`, or an operator, found `;`
  --> src/main.rs:26:29
   |
26 |         Some(Val::Foo) => ();
   |                        --   ^ expected one of `,`, `.`, `?`, `}`, or an operator
   |                        |
   |                        while parsing the `match` arm starting here
help: you likely meant to write a match arm block
   |
26 |         Some(Val::Foo) => { (); }
   |                           ^     ^

while for a case where a single statement is found we could also suggest:

error: expected one of `,`, `.`, `?`, `}`, or an operator, found `;`
  --> src/main.rs:26:29
   |
26 |         Some(Val::Foo) => ();
   |                        --   ^ expected one of `,`, `.`, `?`, `}`, or an operator
   |                        |
   |                        while parsing the `match` arm starting here
help: you might have meant to write a match arm expression separator
   |
26 |         Some(Val::Foo) => (),
   |                             ^

Taken from https://twitter.com/mcclure111/status/1364998004852236289