fix import resolver issue on Windows

[FredKSchott]

Changes

• Resolves Backward slash in webmodules path on Windows #687
• 76dbafc#diff-f91a146b2dcfdeed6a1841e72afd35a3R78 introduced a regression where importResolver would return a windows path instead of a valid URL import.
• This PR reverts that change, and then handles the original Windows issue in a new location, outside of the import resolver.

Testing

Should be covered by existing tests.

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[drwpow]

Nice! All tests passing.

[francislavoie]

I may be wrong, but I think this caused a regression to the fix in #698

With 2.7.4 I get:

import React from "web_modules/react.js";

With 2.7.5 (with the fix from #698) I get:

import React from "./web_modules/react.js";

But with 2.7.6 I get:

import React from "web_modules/react.js";

[drwpow]

I may be wrong, but I think this caused a regression to the fix in #698

Bah! You’re right. Adding a test for it.