[ide_completion] render if a function is async/const/unsafe in completion details

[jhgg]

this change renders in the autocomplete detail, whether a function is async/const/unsafe.

i found myself wanting to know this information at a glance, so now it renders here:

[Veykril]

While I do think this is useful information, I fear that this might become too much information for the detail view(that is when not expanding the view).

Best way to realize whether that is the case or not is to just experiment with it though I think, so let's merge and see.

bors r+

[bors]

Build succeeded:

• Rust (macos-latest)
• Rust (ubuntu-latest)
• Rust (windows-latest)
• TypeScript (ubuntu-latest)
• TypeScript (windows-latest)

[jhgg]

Luckily I think the pathological case of const async unsafe fn is very rare in practice, so this should probably never be a problem practically.