fix: validate Build-protobuf-Library arguments and add smoke tests

[AdamMomen]

Summary

• Added a validation for Build-protobuf-Library.ps1 arguments (Platform, Architecture, BuildType) against allowed values.
• Made argument matching case‑insensitive and normalize to canonical casing.
• Added a -DryRun switch so we can exercise argument handling and directory creation without performing a full protobuf build.
• Introduced a PowerShell smoke test script to guard against regressions of issue #81.
  Details

Tests

Run the smoke tests from the repo root:

pwsh third-party/scripts/Test-Build-protobuf-Library.ps1

This script verifies:

• Incomplete/invalid arguments fail with a non‑zero exit code and do not create bogus *-web-- directories.
• Lowercase but fully specified arguments (web wasm32 release -DryRun) work and create the correct canonical directories.
• Canonical arguments (Web WASM32 Release -DryRun) continue to behave as expected.
• Non‑Web platform example (linux arm64 release -DryRun) is accepted and normalized correctly.

[CLAassistant]

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