Update set what-if handling

[tgauth]

PR Summary

• adds whatIfArg within set block in manifest
• adds deprecation warning when what-if block in manifest is used and removes what-if from capabilities for dsc list
• splits process_args() into process_get_args() and process_set_delete_args()

PR Context

• fix Add new arg type for set and delete to support what-if #1361 (delete PR to follow)

[Copilot]

Pull request overview

This PR updates the handling of what-if functionality in DSC by introducing a new whatIfArg parameter within the set block of resource manifests, deprecating the standalone whatIf block, and refactoring argument processing to distinguish between get/test operations and set/delete operations.

Changes:

• Introduces whatIfArg within set/delete blocks to enable native what-if support
• Adds deprecation warning for resources using the legacy whatIf block and removes WhatIf capability from dsc list output
• Splits process_args() into process_get_args() and process_set_delete_args() to handle different argument types

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
tools/dsctest/dsctest.dsc.manifests.json	Adds test manifest for Test/WhatIfArgKind resource demonstrating new whatIfArg usage
lib/dsc-lib/src/extensions/discover.rs	Updates to use process_get_args and GetArgKind type
lib/dsc-lib/src/dscresources/resource_manifest.rs	Splits ArgKind into GetArgKind and SetDeleteArgKind, adds WhatIf variant to latter
lib/dsc-lib/src/dscresources/command_resource.rs	Refactors argument processing and updates what-if execution logic to check for native support
lib/dsc-lib/src/discovery/command_discovery.rs	Removes WhatIf capability from being reported in resource discovery
lib/dsc-lib/locales/en-us.toml	Adds deprecation warning message for legacy whatIf operation
dsc/tests/dsc_whatif.tests.ps1	Adds tests for new WhatIfArgKind functionality and synthetic what-if
dsc/src/subcommand.rs	Removes WhatIf capability indicator from resource list output

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