Fix built-in contract imports

Description

Flix generate command was failing on scripts/transactions that import built-in contracts like Crypto.

Example of such script:

import Crypto

transaction(key: String, signatureAlgorithm: UInt8, hashAlgorithm: UInt8, weight: UFix64) {
    prepare(signer: auth(BorrowValue, Storage) &Account) {
        pre {
            signatureAlgorithm >= 1 && signatureAlgorithm <= 3: "Must provide a signature algorithm raw value that is 1, 2, or 3"
            hashAlgorithm >= 1 && hashAlgorithm <= 6: "Must provide a hash algorithm raw value that is between 1 and 6"
            weight <= 1000.0: "The key weight must be between 0 and 1000"
        }

        let publicKey = PublicKey(
            publicKey: key.decodeHex(),
            signatureAlgorithm: SignatureAlgorithm(rawValue: signatureAlgorithm)!
        )

        let account = Account(payer: signer)

        account.keys.add(publicKey: publicKey, hashAlgorithm: HashAlgorithm(rawValue: hashAlgorithm)!, weight: weight)
    }
}

Example output in Flow CLI:

❌ Command Error: could not generate flix no contract name found in string

onflow / flixkit-go

Fix built-in contract imports #78

Description