Import specifier deshadowing fix

[guybedford]

This fixes #1910.

The main fix is just the line in src/Chunk.ts, but in the process this exposed an idempotency bug in the deshadowing process itself in that safeName results from previous deshadowing runs can affect future runs.

I've fixed the idempotency bug with a reliable but hacky approach for now, hopefully we can put some thought to something better here, but correctness comes first I feel. Just let me know if I can help explain it at all further.

[guybedford]

(To explain the idempotency bug - it is that the iife format run which comes after the es run would have Sticky$$1 as the function deshadowing name, when the deshadowing is unnecessary for this render run, since the safeName would have been left over from a previous run. Ideally the safeName data would be a separate layer or entirely cleared between runs, but a full reset iteration seems like a performance loss.)

[lukastaegert]

I see what you mean. I think this is not too bad for now but yes, this is a weird interaction between different runs we should probably fix more substantially at some point. Good catch, though 👍