feat(abstract-utxo): export UtxoCoinName types and type guards

BTC-3011

Export the following from @bitgo/abstract-utxo main entry point:
- UtxoCoinName, UtxoCoinNameMainnet, UtxoCoinNameTestnet types
- isUtxoCoinName, isUtxoCoinNameMainnet, isUtxoCoinNameTestnet type guards
- utxoCoinsMainnet, utxoCoinsTestnet constants

This allows consumers to properly type check coin names instead of
using `as any` casts when calling functions like getTransactionExplanation.

TICKET: BTC-3011

Author: lcovar

modules/abstract-utxo/src/index.ts

@@ -1,6 +1,7 @@
 export * from './abstractUtxoCoin';
 export * from './address';
 export * from './config';
+export * from './names';
 export * from './recovery';
 export * from './transaction/fixedScript/replayProtection';
 export * from './transaction/fixedScript/signLegacyTransaction';