Add Solana impl-specific error codes and add ProviderErrorUnion

- ProviderErrorUnion is to be used for shared mojo API which might
  return a specific type of ProviderError, such as SolanaProviderError.
- Also remove ETH in the ID of some sharable strings.

android/java/org/chromium/chrome/browser/crypto_wallet/fragments/ApproveTxBottomSheetDialogFragment.java

@@ -362,7 +362,7 @@ public class ApproveTxBottomSheetDialogFragment extends BottomSheetDialogFragmen
         txService.approveTransaction(CoinType.ETH, mTxInfo.id, (success, error, errorMessage) -> {
             assert success;
             Utils.warnWhenError(ApproveTxBottomSheetDialogFragment.TAG_FRAGMENT,
-                    "approveTransaction", error, errorMessage);
+                    "approveTransaction", error.getProviderError(), errorMessage);
             if (!success) {
                 return;
             }