Use Bech32-encoded state controller and governor addresses

[cycraig]

Description of change

Changes the address type in IotaDocumentMetadata from bee_block::address::Address to a Bech32-encoded String. This is to avoid a hard dependency on bee_block.

Also adds some missing convenience getters in the Wasm bindings.

Links to any relevant issues

Fixes --non-default-features failing in #1042.

Type of change

• Breaking change (fix or feature that would cause existing functionality to not work as expected)

How the change has been tested

Updated unit test.

Change checklist

• I have followed the contribution guidelines for this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

[PhilippGackstatter]

Looks good to me!

[olivereanderson]

Looks good to me.

Would be great if you could take the time to update the test suite of IotaDID to reflect the new behaviour of IotaDID::parse (my bad for not covering casing when I wrote those tests).