fix: is.class for minified class expression

[tgriesser]

Ran into a situation recently where code was working in development, but then exhibited different behavior after the code was run through a minifier. Narrowed it down to the is.class check, which incorrectly assumes there is always trailing whitespace after the class keyword. In a class expression with an anonymous class, class{... is valid syntax.

I initially tried adding the failing test case to test/test.ts but it seems the tsimp is somehow modifying the source and that the whitespace is re-added after the class keyword. I didn't dig into it, and instead added a test/test-node.js with a note about why it was needed.

Edit: Thought of another way to keep the whitespace from being mangled in transpilation, returning the class from a Function constructor. This way there's no .js / separate files for the tests.