Improve derive macro helper input tokens span

I noticed that once the generated result contains a span from the helper, all call-sites in the derived macro will point to every argument tt of the helper

This makes it difficult to goto-define and view hover in helpers

#[derive(serde::Serialize)]
struct Foo {
    #[serde(skip_serializing_if = "Option::is_none")]
    x: Option<i32>,
}

Cursor on is_none hover to output a large amount, such as extern crate serde
And the goto-definition also has multiple results pointing to the inside of the serde

Currently, call-site be obtained on is_none.
Expected to be obtained on the helper name (serde) instead of the helper argument (skip_serializing_if and "Option::is_none")

Start by reproducing the derive-macro example with serde and inspect rust-analyzer's handling of helper input tokens and call-site spans; the issue names no source file or test. Done means hover and goto-definition on is_none resolve using the helper name span, such as serde, rather than the helper arguments.