support namespace syntax

[davidfirst]

This bug is for both: scss and sass detectors.
To reproduce, create a file with the following content: @use "src/corners" as c;.
The detector returns the following: [ 'src/corners', 'as', 'c' ] instead of just ['src/corners'].

See here about this syntax:
https://sass-lang.com/documentation/at-rules/use/#choosing-a-namespace