`Implement missing members` generates without spaces between `*const` and `::` in type name.

// ::core::primitive::i32 is for example.
// these has no spaces between *const and ::core::primitive::i32 but pass `cargo check`.
trait A {
    fn a(a: *const::core::primitive::i32);
    fn b(a: *mut::core::primitive::i32);
    fn c(a: &mut::core::primitive::i32);
}

struct B;
impl A for B {}

After I writing this, Implement missing members generates impl A for B like this:

// these has no space between *const and core::primitive::i32 .
impl A for B {
    fn a(a: *constcore::primitive::i32) {
        todo!()
    }

    fn b(a: *mutcore::primitive::i32) {
        todo!()
    }

    fn c(a: &mutcore::primitive::i32) {
        todo!()
    }
}

rust-analyzer version: (eg. output of "Rust Analyzer: Show RA Version" command)
rust-analyzer version: 02904e99a 2022-02-14 stable

rustc version: (eg. output of rustc -V)
rustc 1.58.1 (db9d1b20b 2022-01-20)
rustc 1.60.0-nightly (e646f3d2a 2022-02-10)

relevant settings: (eg. client settings, or environment variables like CARGO, RUSTUP_HOME or CARGO_HOME)
CARGO, RUSTUP_HOME, CARGO_HOME: Not set.
Installed from rustup-init.exe

VSCode:
Version: 1.64.2 (system setup)
Commit: f80445acd5a3dadef24aa209168452a3d97cc326
Date: 2022-02-09T22:02:28.252Z
Electron: 13.5.2
Chromium: 91.0.4472.164
Node.js: 14.16.0
V8: 9.1.269.39-electron.0
OS: Windows_NT x64 10.0.19043

Start at the “Implement missing members” assist entry point and reproduce the issue with the Rust trait example in the report. Inspect the generated signatures for raw pointers and references, then verify that the output separates the type keyword from the following path and remains accepted by cargo check.