[Optimization] Optimize the error messages that appear when using TypeSpec VS Code Extension in an environment without Node.js/ .NET

[jianingwang123]

Description:
When using the TypeSpec VS Code Extension in an environment without Node.js/.NET , the error messages that appear are not very clear or specific. They lack clear direction and are insufficient for users to quickly and easily understand the problom.

• Scenario1: When installing the TypeSpec VS Code Extension in an environment without Node.js, the error messages as follows:
  picture1:
  

• Scenario2: When using the TypeSpec VS Code Extension to generate .NET code in an environment without .NET, the error messages as follows:
  picture2：
  

Repro steps:

1. Make sure there is no Node.js/ .NET in the environment.
2. Install the TypeSpec VS Code Extension.
3. Open the OUTPUT column of vscode and you can see picture1 error.
4. Install Node.js and typespec compiler.
5. Use >TypeSpec: Generate from TypeSpec command and choose to generate from .Net client code emiiter.
6. Open the OUTPUT column of vscode and you can see picture2 error.

Environment:

• Without Node.js/ .NET
• OS: Windows, Linux

Expected behavior:
Error messages should be clear and specific, prompting users to install Node.js/ .NET . The recommended examples are as follows:

@RodgeFu, @msyyc and @chunyu3 for notification.