Support CPI to other BPF programs

[buffalojoec]

Because of this little hack, CPI only works to builtin programs right now.

mollusk/harness/src/lib.rs

Lines 57 to 58 in 29ebb8c

	const PROGRAM_ACCOUNTS_LEN: usize = 1;
	const PROGRAM_INDICES: &[u16] = &[0];

We'll need to add some logic to extract program accounts, similar to:

https://github.com/anza-xyz/agave/blob/2443048c5cd926581fdc2a26a25006120d16477c/svm/src/transaction_processor.rs#L492

Note this would also involve adding the target BPF program to the cache.