Improves memory handling in TWAnyAddress

[optout21]

Describe the bug Not really a bug: create a class to automatically handle deallocation of TWAnyAddress object.

Additional context https://github.com/trustwallet/wallet-core/blob/master/src/interface/TWAnyAddress.cpp#L16

struct TWAnyAddress {
    TWString* address;
    enum TWCoinType coin;
};

void TWAnyAddressDelete(struct TWAnyAddress* _Nonnull address) {
    TWStringDelete(address->address);
    delete address;
}

[optout21]

I think I misunderstood the real issue here. Here's how I think it should be:

• There is a TWAnyAddress struct holding an address (incl. coin) ☑️
• Internals of TWAnyAddress should be hidden, should not be visible in the .h file ❗️
• TWAnyAddress can can be created from address string or pubkey ☑️
• Methods to obtain address string / coin from TWAnyAddress (TWAnyAddressDescription, TWAnyAddressCoin) ☑️
• TWAnyAddressDelete to clean up address object when no longer needed ☑️
• Since internals is not visible to outside, std::string can be used to store the string inside the struct. ❗️

So the proposed changes:

• Move definition of internals of TWAnyAddress to the .cpp file
• Change the type of address field from TWString* to std::string