feat: support for installing runtimes separately

[xC0dex]

Description:

This PR adds support for installing .NET runtimes independently of SDKs by introducing a new dotnet-runtime input.
The dotnet-runtime parameter behaves the same way as the dotnet-version parameter.

I tested this action on my project, and it works as expected. The logs can be found here.

This proposal represents an initial approach to addressing the need for installing .NET runtimes separately. I’m fully open to feedback, revisions, or alternative solutions, and it’s absolutely okay if this PR will be closed.

This code was built with the help of AI.

Related issue:

Closes #352

Check list:

• Mark if documentation changes are required.
• Mark if tests were added or updated to cover the changes.

[Copilot]

Pull Request Overview

This PR adds support for installing .NET runtimes independently from SDKs by introducing a new dotnet-runtime input parameter. This enables multi-targeting scenarios where users need one SDK version but multiple runtime versions.

Key changes:

• Added dotnet-runtime input that accepts runtime versions with the same syntax as dotnet-version
• New installRuntime() method that installs both .NET Runtime (Microsoft.NETCore.App) and ASP.NET Core Runtime (Microsoft.AspNetCore.App)
• Refactored quality validation to execute before both SDK and runtime installations

Reviewed Changes

Copilot reviewed 5 out of 7 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
src/setup-dotnet.ts	Added runtime version input handling, refactored quality validation, and integrated runtime installation logic
src/installer.ts	Implemented installRuntime() method to install both .NET and ASP.NET Core runtimes
action.yml	Added dotnet-runtime input definition
README.md	Added documentation for installing additional runtimes and updated version syntax descriptions
tests/installer.test.ts	Added comprehensive test coverage for the new installRuntime() method
dist/setup/index.js	Generated distribution file reflecting the source changes
package-lock.json	Added peer: true markers to dependency entries

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