Fix SuppressMessage CustomRule

[HeyItsGilbert]

PR Summary

Problem: SuppressMessageAttribute failed when using named arguments for RuleSuppressionID. Users could not use syntax like: [SuppressMessage("RuleName", RuleSuppressionId="MyId")]

Root Cause: In RuleSuppression.cs, the named argument parser had two bugs:

1. Checked if RuleName was set instead of RuleSuppressionID
2. Assigned the value to RuleName instead of RuleSuppressionID

This broke selective rule suppression for custom rules.

Solution:

• Fixed conflict check to validate RuleSuppressionID instead of RuleName
• Fixed assignment to set RuleSuppressionID instead of RuleName
• Added comprehensive tests for named argument syntax
• Added tests based on repro case.
• Minor formatting improvements

Now both syntaxes work correctly:
[SuppressMessage("Rule", RuleSuppressionId="Id", Scope="Function")]
[SuppressMessage("Rule", "Id", Scope="Function")]

Fixes #1686

PR Checklist

• PR has a meaningful title
  • Use the present tense and imperative mood when describing your changes
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header
• Make sure you've added a new test if existing tests do not effectively test the code changed and/or updated documentation
• This PR is ready to merge and is not Work in Progress.
  • If the PR is work in progress, please add the prefix WIP: to the beginning of the title and remove the prefix when the PR is ready.

[Copilot]

Pull request overview

This PR fixes a critical bug in the RuleSuppression attribute parser that prevented the use of named argument syntax for RuleSuppressionId. The bug caused [SuppressMessage("Rule", RuleSuppressionId="Id")] to fail, particularly affecting custom rules that use targeted suppression via RuleSuppressionID.

Key Changes:

• Fixed the named argument parser to check and assign RuleSuppressionID instead of incorrectly checking/assigning RuleName
• Added comprehensive test coverage for named argument syntax, mixed positional/named arguments, and custom rule scenarios
• Minor formatting improvements to test file (consistent whitespace in script blocks and preprocessor directives)

Reviewed changes

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

File	Description
Engine/Generic/RuleSuppression.cs	Fixed two bugs in the named argument parser for RuleSuppressionID (lines 196, 201) and minor preprocessor directive formatting
Tests/Engine/RuleSuppression.tests.ps1	Added 3 new comprehensive tests for named argument syntax including custom rule scenario, plus consistent whitespace formatting improvements

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