feat: Add --what-if for Microsoft.Windows/FirewallRuleList

[Gijsreyn]

PR Summary

This pull request adds --what-if support for Microsoft.Windows/FirewallRuleList. It also updates the SKILL.md file for re-usability across other resources created.

PR Context

Partially addresses #1529

[Copilot]

Pull request overview

Adds first-class --what-if support for the built-in Microsoft.Windows/FirewallRuleList resource by wiring the manifest to pass a what-if flag through to windows_firewall set, projecting state instead of mutating, and surfacing what-if messages via _metadata.whatIf. Also extends the skill documentation with a reusable what-if implementation/testing pattern.

Changes:

• Resource manifest: add whatIfArg and whatIfReturns for the set operation, plus schema support for _metadata.whatIf.
• Resource implementation: add -w/--what-if parsing and implement non-mutating projections (create/update/delete) with localized what-if messages.
• Tests/docs: add a Pester suite for what-if and expand .github/skills/create-dsc-resource/SKILL.md with what-if guidance.

Reviewed changes

Copilot reviewed 7 out of 7 changed files in this pull request and generated 6 comments.

Show a summary per file

File	Description
resources/windows_firewall/windows_firewall.dsc.resource.json	Wires DSC what-if invocation (whatIfArg, whatIfReturns) and extends schema with _metadata.whatIf.
resources/windows_firewall/src/main.rs	Parses -w/--what-if and passes it into set_rules.
resources/windows_firewall/src/firewall.rs	Implements what-if behavior by projecting results instead of mutating and emitting _metadata.whatIf messages for create/remove.
resources/windows_firewall/src/types.rs	Adds _metadata model (Metadata) to the rule type for what-if message payloads.
resources/windows_firewall/locales/en-us.toml	Adds localized what-if strings for create/remove messages.
resources/windows_firewall/tests/windows_firewall_whatif.tests.ps1	Adds Pester coverage for what-if create/update/delete/multi-rule behavior.
.github/skills/create-dsc-resource/SKILL.md	Documents a standardized what-if pattern for manifests, implementation, localization, and tests.

[SteveL-MSFT]

Great job on adding the SKILL.md update!

[SteveL-MSFT]

Since most resources won't also be used as CLI tools (although technically they could), would prefer to advise agent to use long form in the manifest --what-if as it makes it more obvious to a human reading the manifest