Remove Typescript enums

[mcintyre94]

We'd probably be better off not using typescript enums, due to them compiling to a slightly complex reverse-mapped function type, and also not being helpful when logged (which we generally try to be with eg our Address type).

We use enums currently for:

export enum Endian {
    Little,
    Big,
}

• I'd guess that this could just be a union "Little" | "Big"

export enum AccountRole {
    // Bitflag guide: is signer ⌄⌄ is writable
    WRITABLE_SIGNER = /* 3 */ 0b11, // prettier-ignore
    READONLY_SIGNER = /* 2 */ 0b10, // prettier-ignore
    WRITABLE =        /* 1 */ 0b01, // prettier-ignore
    READONLY =        /* 0 */ 0b00, // prettier-ignore
}

• This would be more useful with string values so that when we log a transaction message instruction account it is legible. We'd need to convert it when compiled though, and would also need to think about the bitshifting used to convert roles etc

export enum OffchainMessageContentFormat {
    RESTRICTED_ASCII_1232_BYTES_MAX = 0,
    UTF8_1232_BYTES_MAX = 1,
    UTF8_65535_BYTES_MAX = 2,
}

This can probably also just a union of strings.

[dpsi9]

Implemented the Endian and OffchainMessageContentFormat changes by removing enum usage and switching to string-based representations with numeric encoding where needed. AccountRole left for a follow-up.