Skip parenthesis if `.` makes statement boundary unambiguous
There is a rule in the parser that statements and match-arms never end in front of a `.` or `?` token (except when the `.` is really `..` or `..=` or `...`). So some of the leading subexpressions that need parentheses inserted when followed by some other operator like `-` or `+`, do not need parentheses when followed by `.` or `?`.
Example:
```rust
fn main() {
loop {}.to_string() + "";
match () {
_ => loop {}.to_string() + "",
};
}
```
`-Zunpretty=expanded` before:
```console
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
fn main() {
(loop {}).to_string() + "";
match () { _ => (loop {}).to_string() + "", };
}
```
After:
```console
#![feature(prelude_import)]
#[prelude_import]
use std::prelude::rust_2021::*;
#[macro_use]
extern crate std;
fn main() {
loop {}.to_string() + "";
match () { _ => loop {}.to_string() + "", };
}
```
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