[diagnostic] replace `<expr> == true` with `<expr>` and `<expr> == false` with `!<expr>`

Also as a degenerate case, !true and !false should become false and true respectively.
As a secondary case, != should do the opposite? At this point I feel like there's another issue but I can't find it.
This should probably only trigger if <expr> evaluates to bool (or !) and has no type errors because:

enum MyBool {
    True,
    False,
}

impl PartialEq<bool> for MyBool {
    fn eq(&self, other: &bool) -> bool {
        match self {
            Self::True => *other,
            Self::False => !*other,
        }
    }
}

fn foo() {
    // compiles
    if MyBool::True == false {
        panic!("True == false");
    }

    // doesn't compile: (`core::ops::Not` not implemented)
    // note that even if `core::ops::Not` was implemented, it probably wouldn't be 
    // if !MyBool::True {}

    // compiles
    if MyBool::True == true {}

    // doesn't compile: (expected `bool`)
    // if MyBool::True {}
}

but, when reviewing code today, I saw a surprising amount of code that is literally just <some expr that evals to bool> == false

No files, tests, or entry points are named; begin by locating rust-analyzer's existing diagnostic implementations and their tests for boolean expressions. Define the supported cases from the issue, including type checking and avoiding type-error expressions, then add focused tests for the requested rewrites; the handling of != remains an unresolved design question.