Fix generated code compilation errors when any description contains newlines

[Copilot]

Multiline Description values on [Command], [CommandOption], or [CommandParameter] produced invalid generated code (*.Descriptor.g.cs), failing with CS1010: Newline in constant. The generator's string escaping only handled backslashes and quotes, leaving embedded newlines as literal line breaks inside the emitted string literal.

• CliFx.Generators/Utils/CSharp.cs: replaced the hand-rolled Escape/Encode logic with Microsoft.CodeAnalysis.CSharp.SymbolDisplay.FormatLiteral, which correctly escapes newlines and all other special characters when producing string literals. Removed the now-unused Escape method.
• CliFx.Tests/HelpSpecs.cs: added a regression test compiling a command with multiline Description (via raw string literal and \n) on [Command], [CommandOption], and [CommandParameter], asserting the help output renders correctly.

Example that now compiles correctly:

[Command("example", Description = """
    here is line 1

    here is line 2
    """)]
public partial class ExampleCommand : ICommand { ... }

• Fixes Multiline Description on [Command] / [CommandOption] / [CommandParameter] produces uncompilable generated code #192

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 90.50%. Comparing base (c43c4d1) to head (982c8d8).

Additional details and impacted files

@@            Coverage Diff             @@
##            prime     #193      +/-   ##
==========================================
- Coverage   90.50%   90.50%   -0.01%     
==========================================
  Files          66       66              
  Lines        2339     2338       -1     
  Branches      282      282              
==========================================
- Hits         2117     2116       -1     
  Misses        140      140              
  Partials       82       82              

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[Copilot]

🟡 Changes recommended

The generator’s Encode(char?) still emits unescaped char literals, which can produce invalid generated C# for certain short-name values.

Once you've addressed the issues Copilot identified, you can request another Copilot review.

Pull request overview

This PR fixes a source-generator bug where multiline Description values (on [Command], [CommandOption], and [CommandParameter]) could produce uncompilable generated descriptor code due to raw newline characters in emitted string literals.

Changes:

• Switched generator string literal encoding to Roslyn’s SymbolDisplay.FormatLiteral to correctly escape newlines and other special characters.
• Added a regression test that compiles commands with multiline descriptions and validates the resulting help output contains the expected text.

File summaries

File	Description
CliFx.Generators/Utils/CSharp.cs	Updates string encoding in generated code to use Roslyn literal formatting for correct escaping.
CliFx.Tests/HelpSpecs.cs	Adds a regression test covering multiline descriptions on command/option/parameter metadata.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 1
• Review effort level: Lite

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