feat: cspell-glob matches only files under the root (#913)

For historical reasons, cspell-glob assumed two roots:
1. the one passed in which defaulted to the current working directory
2. the FS root on any drive.

This happened because it was sometimes difficult to determine the root inside the VS Code extension.

In cspell 5, there is a shift with the `ignorePaths` meaning to be relative to the location of the file that defined them.

It will also be possible to define the root for the `ignorePaths` within the configuration file.