fix(js): use outDir to avoid ambient type definition creation

[IanVS]

Fixes one of the issues reported in #985.

This generates the same kind of definition files as @docsearch/react, not ambient (global) definitions that were being produced previously, which were incorrect (see reproduction: https://stackblitz.com/edit/typescript-decjve?file=index.ts).

I tested this by copying the new dist folder into the node_modules of my own project, and the type error disappeared.

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[IanVS]

Here's a modified CSB based on the bot's above, that shows the issue is resolved: https://codesandbox.io/s/vanilla-forked-s6o0zl?file=/src/index.ts

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Thanks! ☺️