Update `ExpandAliasHandler` to use latest PowerShell parser

[andyleejordan]

Prerequisites

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• I have searched all issues to ensure it has not already been requested.

Summary

In the following code we (repeatedly) define an internal PowerShell script that uses the original parser to expand the alias.

PowerShellEditorServices/src/PowerShellEditorServices/Services/PowerShell/Handlers/ExpandAliasHandler.cs

Lines 32 to 71 in 37f0648

	public async Task<ExpandAliasResult> Handle(ExpandAliasParams request, CancellationToken cancellationToken)
	{
	const string script = @"
	function __Expand-Alias {
	[System.Diagnostics.DebuggerHidden()]
	param($targetScript)
	[ref]$errors=$null
	$tokens = [System.Management.Automation.PsParser]::Tokenize($targetScript, $errors).Where({$_.type -eq 'command'}) |
	Sort-Object Start -Descending
	foreach ($token in $tokens) {
	$definition=(Get-Command ('`'+$token.Content) -CommandType Alias -ErrorAction SilentlyContinue).Definition
	if($definition) {
	$lhs=$targetScript.Substring(0, $token.Start)
	$rhs=$targetScript.Substring($token.Start + $token.Length)
	$targetScript=$lhs + $definition + $rhs
	}
	}
	$targetScript
	}";
	// TODO: Refactor to not rerun the function definition every time.
	PSCommand psCommand = new();
	psCommand
	.AddScript(script)
	.AddStatement()
	.AddCommand("__Expand-Alias")
	.AddArgument(request.Text);
	System.Collections.Generic.IReadOnlyList<string> result = await _executionService.ExecutePSCommandAsync<string>(psCommand, cancellationToken).ConfigureAwait(false);
	return new ExpandAliasResult
	{
	Text = result[0]
	};
	}

Proposed Design

This should be updated to use the new parser directly from the PowerShell APIs in C# and return a proper edit (potentially deprecating the need for an entirely separate custom request).

[andyleejordan]

FYI @SeeminglyScience

[andyleejordan]

Actually, are we certain that useLocalScope is defaulting to true? I was looking at the code and that doesn't appear to be the case. The second argument is isScript.

[andyleejordan]

Related PowerShell/vscode-powershell#338