extendable param files intellisense for shared bicepparam files

[polatengin]

Fixes #14519

Description

This PR adds full IntelliSense support for base in .bicepparam files that use extends statements, including both symbol completion (base) and member completion (base.<param>, nested object and array item members).

Example Usage

// main.bicep
param one string = ''
param two string = ''
param three string = ''
param four object = {
  name: ''
  value: ''
}
param five array = [
  {
    name: ''
    value: ''
  }
]

// shared.bicepparam
using none
param three = 'param three'
param four = {
  name: 'param four'
}
param five = [
  {
    name: 'param five'
  }
]

// main.bicepparam
using 'main.bicep'
extends 'shared.bicepparam'
param one = 'param one'
param two = base.three
param four = base.four
param five = [
  base.five[0]
]

Expected devex with this PR:

• base is suggested in completion when extends is present
• base. suggests inherited assignments from the extended params file
• base.four. suggests object properties (e.g. name)
• base.five[0]. suggests array item object properties

Checklist

• I have read and adhere to the contribution guide.

Microsoft Reviewers: Open in CodeFlow

[github-actions]

Test this change out locally with the following install scripts (Action run 22279815439)

VSCode

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-vsix.sh) --run-id 22279815439

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-vsix.ps1) } -RunId 22279815439"

Azure CLI

• Mac/Linux

  bash <(curl -Ls https://aka.ms/bicep/nightly-cli.sh) --run-id 22279815439

• Windows

  iex "& { $(irm https://aka.ms/bicep/nightly-cli.ps1) } -RunId 22279815439"