SVM: account_loader.rs generic over SVMMessage

[apfitzge]

Problem

#2109 - for SVM to be generic over transaction/message type, account_loader.rs must be generic over the traits

Summary of Changes

• Make functions in account_loader.rs generic over SVMMessage

Fixes #2109

[buffalojoec]

Woohoo!

[LucasSte]

The original decompile_instructions function is also used in benchmarks and some tests. Have you considered adding it to your trait?

I am thinking that these new lines may become repeated code at some point.

[apfitzge]

I originally had it as a function, but the only part in actual code it was called was here. Removed as part of the trait simplification.

But also wanted to remove the allocation that BorrowedInstruction requires:

pub struct BorrowedInstruction<'a> {
    pub program_id: &'a Pubkey,
    pub accounts: Vec<BorrowedAccountMeta<'a>>, //<-- allocation here
    pub data: &'a [u8],
}

In this first step I'm just doing a drop-in replacement where we still do this allocation.
As a follow-up I will write a version of construct_instructions_data (and its' input) that require no allocations).
This was the reasoning I had behind not having this as part of the trait.

[apfitzge]

rebased on master to remove the dependency add commit - last time I relied on auto-merging it seemed to break CI: see #2388