lang: Support [T; N] in account structs for primitive field T

[cherryman]

No description provided.

[mgild]

Current error

#[derive(Clone, Copy, AnchorSerialize, AnchorDeserialize)]
pub struct Array<T, const S: usize> {
    data: [T; S],
    len: usize
}

thread 'main' panicked at 'called `Result::unwrap()` on an `Err` value: ParseIntError { kind: InvalidDigit }', lang/syn/src/idl/mod.rs:162:78
stack backtrace:
   0: _rust_begin_unwind
   1: core::panicking::panic_fmt
   2: core::result::unwrap_failed
   3: <anchor_syn::idl::IdlType as core::str::traits::FromStr>::from_str
   4: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
   5: core::ops::function::impls::<impl core::ops::function::FnMut<A> for &mut F>::call_mut
   6: <core::iter::adapters::ResultShunt<I,E> as core::iter::traits::iterator::Iterator>::next
   7: anchor_syn::idl::file::parse_ty_defs
   8: anchor_syn::idl::file::parse
   9: anchor_cli::build_cwd
  10: anchor_cli::build
  11: anchor_cli::entry
  12: anchor::main
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.

[dovahcrow]

Can we have an attribute attached to a field in the account saying that this field is opaque to idl, e.g. #[idl(skip)] my_field: [T; N]. Although this forbids javascript to read the content of that field, at least we can use generics and const generics in anchor program.

[acheroncrypto]

Added in #2824.