Fix PowerShell script encoding, regex specificity, and version validation

[Copilot]

Addresses code review feedback on the OpenAPI Generator update automation script to fix encoding issues, prevent unintended hash replacements, and improve version format validation.

Changes

• Encoding fixes: All Set-Content calls now specify -Encoding UTF8 and remove -NoNewline to prevent UTF-16 rewrites on Windows PowerShell 5.1 and preserve trailing newlines

• Regex specificity: Hash replacements in Resource.Designer.cs now use (?s)(OpenApiGenerator_MD5.*?Looks up a localized string similar to )[0-9a-f]{32}(\.) to scope replacements to the correct resource blocks and avoid overwriting SwaggerCodegenCli/LegacyOpenApiGenerator hashes

• Version validation: Added format validation (3-part semver), numeric component checks, and warnings for multi-digit minor/patch versions that may break enum naming assumptions

# Before: Silent encoding changes, broad regex, no validation
Set-Content $file $content -NoNewline
$content -replace '(Looks up.*?)[0-9a-f]{32}(\.)', "`${1}$MD5`${2}"

# After: Explicit UTF-8, scoped regex, validated input
Set-Content $file $content -Encoding UTF8
$content -replace '(?s)(OpenApiGenerator_MD5.*?Looks up.*?)[0-9a-f]{32}(\.)', "`${1}$MD5`${2}"
if ($newMinor.Length -gt 2) { Write-Warning "Multi-digit version..." }

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