Fix completion item text selection priority

[heavenshell]

Hi,

I found vtslp and typescript-language-server complete invalid item.

Steps to reproduce

type Address = {
  state?: string
  town?: string
}

type Person = {
  name?: string
  age?: number
  address?: Address
}

const foo: Person = {
  name: 'foo',
  age: 20,                 
}

When I type like following

foo.address.<c-x><c-o>
            +--------------+
            | state? field |
            | town?  field |
            +--------------+

and select state?, text insert like following

foo.address.?.state

expected behavior is

foo.address?.state

According to the Language Server Protocol 3.17 specification:

• filterText is only used for filtering and sorting completion items
• When textEdit is provided, insertText must be ignored

In vim-lsp completion context, l:completion_item['filterText'] was set.
I think this is unnecessary.

I would appreciate it if someone could review this.

Before

Kapture.2025-08-10.17.11.10.mp4

After

Kapture.2025-08-10.17.38.26.mp4