[ENG] Fix namespace collision between src and generated submodule

[NoriZC]

Description

This pull request introduces changes to improve how namespaces are handled in the build scripts and templates for the Az modules. The most important updates include adding support for reading the RootNamespace from .csproj files, passing the namespace to template generation, and updating the template to include a placeholder for the namespace.

This could help resolve the issue in
#27943
#28101

Mandatory Checklist

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• Check this box to confirm: I have read the Submitting Changes section of CONTRIBUTING.md and reviewed the following information:

• SHOULD update ChangeLog.md file(s) appropriately
  • Update src/{{SERVICE}}/{{SERVICE}}/ChangeLog.md.
    • A snippet outlining the change(s) made in the PR should be written under the ## Upcoming Release header in the past tense.
  • Should not change ChangeLog.md if no new release is required, such as fixing test case only.
• SHOULD regenerate markdown help files if there is cmdlet API change. Instruction
• SHOULD have proper test coverage for changes in pull request.
• SHOULD NOT adjust version of module manually in pull request

[azure-client-tools-bot-prd]

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[Copilot]

Pull Request Overview

This PR enhances how module namespaces are handled during generation by reading the RootNamespace from existing .csproj files, passing it into the template engine, and updating the template/props files accordingly.

• Added a <RootNamespace> placeholder to the project template.
• Extended the PowerShell build script to extract and forward the namespace into template rendering.
• Removed the hardcoded RootNamespace in Az.autorest.props to allow explicit template insertion.

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
tools/BuildScripts/Templates/Az.ModuleName.csproj	Insert <RootNamespace> placeholder in the template
tools/BuildScripts/BuildScripts.psm1	Parse RootNamespace from .csproj and pass it to the template
src/Az.autorest.props	Remove default <RootNamespace>, deferring to the new template

Comments suppressed due to low confidence (1)

tools/BuildScripts/BuildScripts.psm1:183

• The variable subModuleNameTrimmed is undefined here. It looks like cSubModuleNameTrimmed was assigned above and should be used to construct the path.

    $csprojPath = Join-Path $SourceDirectory "Az.${subModuleNameTrimmed}.csproj"

[Copilot]

When $Namespace is empty or undefined, the placeholder {NamespacePlaceHolder} will remain in the generated .csproj, causing invalid XML. Consider providing a default or emitting an error if the namespace cannot be read.

Suggested change

	if ($Namespace) {
	$templateFile = $templateFile -replace '{NamespacePlaceHolder}', $Namespace
	}
	if (-not $Namespace) {
	Write-Error "Error: Namespace is undefined or empty. Cannot generate valid .csproj file."
	return
	}
	$templateFile = $templateFile -replace '{NamespacePlaceHolder}', $Namespace