Improve panic messages when in `proc_macro`

It can be hard to figure out which `parse_quote!` invocation failed because `-Zmacro-backtrace` is unstable + disabled by default.

What do you think about adding `[file:line:column]` information to `panic!()` messages inside of `parse_quote!` and `parse_quote_spanned!`, and others places where `panic!()` is used?

We would define a `panic!` macro as follows:

```rust
macro_rules! panic {
($message:literal $($tt:tt)*) => {{
#[cfg(feature = "proc-macro")]
let is_available = proc_macro::is_available();
if is_available {
let location = core::panic::Location::caller();
let file = location.file();
let line = location.line();
let column = location.column();
::core::panic!(concat!("[{}:{}:{}] ", $message), file, line, column $($tt)*)
} else {
::core::panic!($message $($tt)*)
}
}};
}
```

Then use it everywhere in the crate.

This will make it easier to debug proc-macros, by turning an error message like this:

```
error: proc-macro derive panicked
--> src/lib.rs:1:10
|
1 | #[derive(Trait)]
| ^^^^^^
|
= help: message: expected string literal
```

Into the following:

```
error: proc-macro derive panicked
--> src/lib.rs:1:10
|
1 | #[derive(Trait)]
| ^^^^^^
|
= help: message: [/tmp/macr/src/lib.rs:9:10] expected string literal
```