feat: show full type in tooltips for hints

[roife]

fix #19615.

[roife]

[roife]

Previously, hovering over any part of a hint would display the complete type.

Now, the certain hidden content is only showed when the mouse hovers over its corresponding ....

[Veykril]

I'd expect something like the following instead

Suggested change

	fn maybe_truncated<T, F: FnOnce(&mut Self) -> T>(&mut self, f: F) -> T {
	let truncated = self.should_truncate() && self.fmt.start_truncated();
	let res = f(self);
	if truncated {
	self.fmt.end_truncated();
	}
	res
	}
	fn maybe_truncated<T, F: FnOnce(&mut Self) -> T>(&mut self, f: F) -> Option<T> {
	if self.should_truncate() {
	let end_truncate = self.fmt.start_truncated();
	if self.fmt.start_truncated() {
	let res = f(self);
	self.end_truncated();
	Some(res)
	} else {
	write!(self, "{TYPE_HINT_TRUNCATION}")
	None
	}
	} else {
	Some(f(self))
	}
	}

This way any writers that don't care about the truncation behavior will have the previous behavior, that is they write the truncation dots as before.

[roife]

So we should limit the behavior of "write dots" within HirFormatter and not leak it into the specific writer, right? I will modify this part.

[roife]

Here we should do three things in end_truncated:

1. Move the contents of last_part to tooltip
2. Write TYPE_HINT_TRUNCATION into last_part
3. Create a new part

Since the second step must be completed after 1 and before 3, we may need to let writer handle it, but I can have end_truncated take a parameter as a placeholder, so that TYPE_HINT_TRUNCATION is not leaked.

If the writer has more complex behavior in the future, we can consider using a closure.

(resolved in bed7a75)