[Elements] Client-side stripping of blinding key for blech32 addresses

Similarly to this, but for blech32 addresses:

https://github.com/Blockstream/esplora/blob/cad3cef99b1a149193e7f02bf515bbdc9851a91e/client/src/util.js#L39-L48

This requires a JavaScript implementation of the blech32 encoding format, which could be based on the [reference Python implementation](https://github.com/ElementsProject/elements/blob/master/test/functional/test_framework/liquid_addr.py) or the [Rust implementation in rust-elements](https://github.com/ElementsProject/rust-elements/pull/16/files#diff-02b0ed4def45fae054d60b6e1f8caf7c).