fix import scanner

[FredKSchott]

Our new import scanner regex was too strict about whitespace, and wasn't properly matching newline characters in statements like these:

import {
    SvelteComponent as e,
    create_component as t,
    destroy_component as n,
    init as o,
    mount_component as r,
    noop as s,
    safe_not_equal as m,
    transition_in as l,
    transition_out as u,
} from '/web_modules/svelte/internal.js';

The /s regex flag does most of the work in this PR, along with some other Regex fixes.

meta point: we're very integration-test heavy (which I like!) but this would be a good area to invest in unit tests of the actual scanner itself.