Modernize alias expansion to use the language parser

[Andy Jordan (andyleejordan)]

Fixes#2108.

The powerShell/expandAlias handler built an embedded PowerShell here-string that called [System.Management.Automation.PsParser]::Tokenize to find command tokens. That legacy tokenizer is Windows PowerShell / full-framework only and carries its parsing limitations.

This rewrites the logic in C# against the modern, cross-edition APIs:

• Tokenize with Parser.ParseInput and select command-name tokens via TokenFlags.CommandName instead of the legacy PSTokenType.Command.
• Resolve every distinct name to its alias definition in a single Get-Command -CommandType Alias round-trip, rather than re-defining a helper function and querying one token at a time.
• Escape wildcard metacharacters with WildcardPattern.Escape so aliases whose names are patterns — ? (Where-Object) and % (ForEach-Object) — resolve to themselves. The old script did this by hand with a leading backtick.
• Rebuild the text by substituting from the highest offset down so earlier extents stay valid as the length changes, preserving behavior for multiple aliases on a line and multi-token definitions.

Scripts with no aliases are returned unchanged, and the JSON-RPC contract (IExpandAliasHandler / powerShell/expandAlias / ExpandAliasParams.Text → ExpandAliasResult.Text) is untouched.

Testing

Extended the E2E tests with a multi-alias line that includes the wildcard-named ? alias — gci | ? Name | % Name → Get-ChildItem | Where-Object Name | ForEach-Object Name — which the naive modern approach would mishandle. Both ExpandAlias E2E tests pass.

[Copilot]

Pull request overview

This PR modernizes the ExpandAliasHandler by replacing a legacy approach that repeatedly defined and executed an internal PowerShell script using the obsolete PsParser tokenizer with a modern implementation that uses the System.Management.Automation.Language.Parser API directly from C#. This addresses issue #2108.

Changes:

• Replaced the inline PowerShell script with C# code that uses Parser.ParseInput to tokenize the input and identify command-name tokens, resolves aliases via a single Get-Command call, and performs backward string substitution using StringBuilder.
• Added proper handling of wildcard metacharacter alias names (like ? and %) via WildcardPattern.Escape.
• Added a new E2E test that exercises multiple aliases on one line, including wildcard metacharacter aliases.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/PowerShellEditorServices/Services/PowerShell/Handlers/ExpandAliasHandler.cs	Rewrote alias expansion to use the modern language parser and C#-native token manipulation instead of an inline PowerShell script with the legacy PsParser.
test/PowerShellEditorServices.Test.E2E/LanguageServerProtocolMessageTests.cs	Added E2E test for expanding multiple aliases (including ? and %) in a single request.

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[Andy Jordan (andyleejordan)]

Well that's an old TODO solved and the tests pass so...

[Justin Grote (JustinGrote)]

Yeah looks fine to me. As a follow-on issue we should probably update the rename handler to use this same code path if it isn't already.