preact/signals: move enum-dependent code to .ts file

[jeffomatic]

This change moves some type definitions in 3rdparty/preact/signals/internal.d.ts into the corresponding .ts file. Specifically, it moves an enum declaration from .d.ts to .ts, and also moves any dependent types.

The reason is that enum is subtly broken in .d.ts files, even if it is const enum. This doesn't cause issues for tsc, but it does cause problems if you're bundling ScriptLib using the source .ts files via a bundler such as esbuild.

To my mind, const enum ought to be fine in a .d.ts file, but the maintainer of esbuild seems to disagree.

It is possible that downstream code is including the types extracted from internal.d.ts, but I think the risk is low. Those types don't seem to be very useful outside of signals/index.ts, so it shouldn't break anything unless the downstream code was doing something really weird.

[jeffomatic]

FWIW, I haven't tried this yet, but it might be possible to reimplement this without an enum using a union of string literals, such as:

type OptionTypes = "_hook" | "_diff" | ...

[CreepGin]

Noted =)