(GH-1696) Add --what-if in MCP server tools

[Gijs Reijn (Gijsreyn)]

PR Summary

This pull request adds --what-if support in MCP server tools.

PR Context

Fixes #1696

[Copilot]

Pull request overview

Adds what_if (dry-run / preview) support to the DSC MCP server tools so AI agents can safely simulate set/delete operations via MCP, aligning server-mode behavior with the CLI’s what-if capability.

Changes:

• Added what_if request parameter handling for invoke_dsc_resource (set/delete) and invoke_dsc_config (set only), mapping to ExecutionKind::WhatIf and returning invalid-params errors for unsupported operations.
• Expanded Pester coverage for MCP server what-if scenarios, including native and synthetic what-if paths.
• Updated i18n strings, docs, and changelog to document the new capability.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
dsc/tests/dsc_server.tests.ps1	Adds end-to-end MCP server tests validating what-if behavior for config/resource set/delete and unsupported ops.
dsc/src/server/invoke_dsc_resource.rs	Introduces what_if request argument; routes set/delete through ExecutionKind::WhatIf and returns appropriate delete result shapes.
dsc/src/server/invoke_dsc_config.rs	Adds what_if request argument for config set by setting configurator context execution type to WhatIf.
dsc/locales/en-us.toml	Adds localized error messages for invalid what_if usage.
docs/concepts/dsc-mcp-server.md	Documents how agents can preview changes using what_if with MCP tools.
CHANGELOG.md	Notes the new MCP what-if support under Unreleased “Added”.

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