feature: Add 'destructure struct binding' assist

[IFcoltransG]

Adds an assist to destructure a struct in a binding. This is part of #8673, but more functionality is needed to bring it in line with tuple bindings. Similar to #9855 for tuple bindings, except that this pull does not yet edit the usages of the fields, just the original binding to an identifier.

struct Struct { a: u8, b: u8 }

fn main() {
    let $0x = Struct { a: 1, b: 2 };
}

->

struct Struct { a: u8, b: u8 }

fn main() {
    let Struct { a: $0_a, b: _b } = Struct { a: 1, b: 2 };
}

Implemented:

• Destructuring record structs, tuple structs and unit structs
• Copying mut and ref from the original identifier to the fields of the struct
• Destructuring within any sort of binding, inline

Not implemented:

• Smart variable naming to ensure no shadowing
• Editing usages
• Destructuring using a sub-pattern
• Omitting private and #[non_exhaustive] fields with ..

[Veykril]

I'm cleaning up our PR backlog right now, if you are coming back to this feel free to re-open.