Implement no-mixed-spaces-and-tabs rule

[jez9999]

As the indent rule is not the equivalent of ESLint's no-mixed-spaces-and-tabs because it doesn't implement smart-tabs (see #268), a new no-mixed-spaces-and-tabs rule should be introduced that allows a "smart-tabs" option.

[keremgocen]

How would one go about implementing a new rule then?:)

[younes-io]

This rule seems to be already implemented (cf. https://eslint.org/docs/rules/no-mixed-spaces-and-tabs)

@buzinas I think the issue can be closed