[Bug] Uppercase driver letter in windows

[funte]

• I'd be willing to submit the fix

Describe the bug

Maybe its not bug but still little annoying. In Vscode ternimal(profile to use cmd.exe or powershell.exe) when using npm build
command, the request from Webpack resolver has a uppercase driver letter, but lowercase when debugging, and they are
different in the CacheBackend._data, so every virtual file webpack-virtual-modules must write twice.

To Reproduce

I create a project show this question at https://github.com/funte/test.
Using Vscode open this project in windows.
Run npm run build command the terminal log path with uppercase driver letter.
Press F5 to debug the terminal log lowercase file path.

Screenshots

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Environment if relevant (please complete the following information):

• OS: [e.g. OSX, Linux, Windows, ...]
• Node version [e.g. 8.15.0, 10.15.1, ...]
• Mochapack version [e.g. 1.1.3, ...]
• Webpack version [e.g. 4.26.1, ...]

Additional context

Add any other context about the problem here.