Fix path handling on Windows

[carlalbrecht]

Closes #10

This PR resolves two issues with path handling on Windows:

• Transform module paths had a leading slash, which caused the error described in https://github.com/sodatea/vite-jest/issues/10#issue-944520897

• Resolved import paths contained unescaped (single) backslashes, which resulted in errors like this:

  FAIL  src/app/App.test.tsx
  ● Test suite failed to run
  
    Cannot find module 'C:UsersCarlcodeprojectname
  rontend
    ode_modules@testing-libraryjest-domdistindex.js' from 'src/setupTests.ts'
  
      at Resolver.resolveModule (node_modules/jest-resolve/build/resolver.js:313:11)

[bencelang]

@sodatea Can you take a look at this? Currently we cannot use this module on Windows at all due to the path handling. This PR looks very promising in terms of fixing that.