swc cannot parse `declare import`s used to declare node builtins in REPL

[cspotcode]

We tell the typechecker that node builtin modules are available in the REPL without importing, using declare import assert = require('assert'); Implemented in #1500

Unfortunately, swc cannot parse declare import and it seems this is because it's technically invalid TS. It achieves the desired effect when using the TS compiler -- we use @ts-ignore to suppress the error -- but I think we'll need to disable it for swc and any third-party transpilers.

We should also consider test coverage of the REPL with swc.

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An alternative syntax I considered when writing #1500:

declare const fs: typeof import('fs');
// @ts-ignore
import type * as fs from 'fs';

I decided against it because if you subsequently attempt to const fs = 123; you get a type error.

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Thinking we'll have to keep the syntax as-is, but disable it when in transpileOnly mode. Implementation notes: since transpileOnly mode is implied by other options, such as swc, we must make sure we have the real answer when checking transpileOnly === true in the REPL.