Gaps in generated types for Typescript (Option and Vec<String>)

[eoin-betdex]

We've run up against two small issues when working in Typescript with the types generated for account fields from the IDLs.

1. Option<T> fields map to unknown type in Typescript when T is one of the standard types defined in TypeMap, e.g.,

#[account]
pub struct MyAccount {
    pub counter: Option<u16>,
}

const accountAddress = "...";
const myAccount = await myProgram.account.myAccount.fetch(accountAddress);
const counterPlusOne = myAccount.counter + 1;  // Assuming the counter has been initialised

Results in TS2365: Operator '+' cannot be applied to types 'unknown' and '1'.

2. Vec<String> fields map to unknown type in Typescript. Only the types defined in TypeMap are considered when determining how to map a Vec<T> to some T'[].