[ecashaddrjs] Add types so typescript apps can import without having to declare

Summary:
Depends on D15399

Add types declaration file and bundle with module so that typescript apps may use ecashaddrjs without having to declare its types.

Test Plan: See draft diff D15392, where this diff's version of ecashaddrjs has been installed, and CI build now passes.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D15400