GeezerVison

PR Summary

PSUseDeclaredVarsMoreThanAssignments now flags unused variables in a multiple assignment such as $a, $b = $null. Before, it only flagged assignments whose left-hand side was a single variable.

• Each variable in an array literal on the left-hand side is now treated like a single-variable assignment. Typed elements such as [int]$a, $b = 1, 2 are covered by the existing ConvertExpressionAst handling.
• When the rule checks whether a variable reference is the assignment itself, it now stops at the first matching variable. Otherwise, with several variables on the left-hand side, the last one would win.
• Each finding uses the whole left-hand side ($a, $b) as its extent, the same as the existing code. The suppression ID is the variable name, so suppressing by name still works.

Fixes #2164

How tested:

• Added three Pester cases to Tests/Rules/UseDeclaredVarsMoreThanAssignments.tests.ps1:
  • both variables flagged
  • only the unused one flagged
  • none flagged when both are used
• The two "flagged" cases fail without the fix: expected 2 got 0, and expected 1 got 0.
• With the fix, UseDeclaredVarsMoreThanAssignments.tests.ps1 passes 32/32 and all of Tests/Rules passes 1742, with 0 failed and 7 skipped (PowerShell 7.6.7, Windows 11).

This only touches AnalyzeScriptBlockAst, so it doesn't conflict with the expression-bodied member changes in #2182.

PR Checklist

• PR has a meaningful title
• Summarized changes
• Change is not breaking
• Make sure all .cs, .ps1 and .psm1 files have the correct copyright header (no new files)
• 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.