fix: do not show raw identifier label in completions

[A4-Tacks]

Example

mod foo {
    pub struct r#if;
    pub struct r#struct<T>;
    pub mod r#mod;
}
type X = foo::$0;

Before this PR

md r#mod::
st if                 r#if
st r#struct<…> r#struct<T>

After this PR

md mod::
st if                 r#if
st struct<…>   r#struct<T>

[ChayimFriedman2]

I actually prefer the old way. But why is if not escaped?

[A4-Tacks]

The old implement is not easy to use, for the following reasons:

1. Inconsistent behavior with other completion items
2. Completing r#struct requires input rstruct instead of struct

Another behavior is to make all labels use r# and 'lookup' without escaping, but this requires changing too much code

And it seems that this PR implementation is now more consistent:

md non_keyword::
md mod::
st if                 r#if
st struct<…>   r#struct<T>
st foo<…>           foo<T>

Rather than:

md non_keyword::
md r#mod::
st r#if               r#if
st r#struct<…> r#struct<T>
st foo<…>           foo<T>

And this PR only removes a small range of raw ident escaping, and the current behavior has not been escaped in most places, so this is a 'fix' PR and improves user experience

[ChayimFriedman2]

Sure, it only inserts r# when needed, like people do in Rust.

And you don't need to type r, it'll work fine if you only type the keyword (since editors fuzzy-match).

[A4-Tacks]

And you don't need to type r, it'll work fine if you only type the keyword (since editors fuzzy-match).

No, I need to type r. I'll reproduce it in coc.nvim, maybe it's because of {"label":"r#struct<…>","filterText":"r#struct"}