Properly escape sharedPath in generated import statements

[Conduitry]

If the sharedPath contains any special characters, the generated import statement is not correctly escaping them. This PR fixes that.

As an added bonus, unit tests pass on Windows again. Previously, the unit tests which used shared were generating

import { things } from 'C:\some\path\svelte\shared.js'

which is the same as 'C:somepathsvelteshared.js', which reify rightfully balked at.

[delbeke]

+1

[barak007]

+1

[Rich-Harris]

thank you!