Only prompt the first matching definition

Does this issue occur when all extensions are disabled?: Yes

• VS Code Version: Version: 1.58.0
• OS Version: macos catalina 10.15.7

Steps to Reproduce:

// package 'A'
export interface IConfig {}

export class Define {
  public config: IConfig
}
 
// -------------------------- //

// package 'B'
// package 'B' - a.ts
declare module 'A' {
  interface IConfig {
    setB1: () => {}
  }
}

// package 'B' - b.ts
declare module 'A' {
  interface IConfig {
    setB2: () => {}
  }
}

// -------------------------- //

// package 'C'
declare module 'A' {
  interface IConfig {
    setC: () => {}
  }
}

// -------------------------- //

// use
import { IConfig, Define } from 'A';

const a: IConfig // no problem, support `setB1` `setB2` `setC`

const b = new Define();
b.config // error, only prompt support for `setB1` method

Is there a way to make b.config prompt for all methods? In addition to using b.config as Iconfig

Reproduce the declaration-merging example from the issue with packages A, B, and C, then compare completion for a direct IConfig value with completion for b.config. Trace the TypeScript language-service or type-checking behavior involved and add a regression test demonstrating that all merged members are offered for b.config.