Fix macro hygiene bug

This fixes rust-lang#32922 (EDIT: and fixes rust-lang#31856), macro hygiene bugs.
It is a [breaking-change]. For example, the following would break:
```rust
fn main() {
    let x = true;
    macro_rules! foo { () => {
        let x = 0;
        macro_rules! bar { () => {x} }
        let _: bool = bar!();
        //^ `bar!()` used to resolve the first `x` (a bool),
        //| but will now resolve to the second x (an i32).
    }}
    foo! {};
}
```

r? @nrc

Rollup of 11 pull requests

- Successful merges: #32923, #32926, #32929, #32931, #32935, #32945, #32946, #32964, #32970, #32973, #32997
- Failed merges:

Fix macro hygiene regression

The regression was caused by #32923, which is currently in beta.

The following is an example of regressed code:
```rust
fn main() {
    let x = 0;
    macro_rules! foo { () => {
        println!("{}", x); // prints `0` on stable and after this PR, prints `1` on beta and nightly
    } }

    let x = 1;
    foo!();
}
```

For code to regress, the following is necessary (but not sufficient):
 - There must be a local variable before a macro in a block, and the macro must use the variable.
 - There must be a second local variable with the same name after the macro.
 - The macro must be invoked in a statement position after the second local variable.

For example, if the `let x = 0;` from the breaking example were commented out, it would (correctly) not compile on beta/nightly. If the semicolon were removed from `foo!();`, it would (correctly) print `0` on beta and nightly.

r? @nrc