Add a way to get stake minimum delegation from RPC

[brooksprumo]

Problem

From RPC, we cannot query the minimum stake delegation.

Proposed Solution

Add a new RPC endpoint.

We cannot use simulate_transaction() here, as it fails when loading accounts.

Previous proposed solution

How about an RpcClient helper under the hood that performs simulate_transaction and returns parsed return_data of type T? I think we're going to want something similar for spl_token::instruction::GetAccountDataSize

Originally posted by @CriesofCarrots in #24690 (comment)

Initial Description

how about moving this into solana-program, so we don’t need a new dep in ledger/
When it’s moved into solana-program, we could probably remove the FeatureSet as well (since that’s only available in solana-sdk) and instead just always use 1 SOL

Originally posted by @mvines in #24660 (comment)

[brooksprumo]

@mvines There is already a get_minimum_delegation() in solana-program here:

solana/sdk/program/src/stake/tools.rs

Lines 13 to 17 in edf3f05

	pub fn get_minimum_delegation() -> Result<u64, ProgramError> {
	let instruction = super::instruction::get_minimum_delegation();
	crate::program::invoke_unchecked(&instruction, &[])?;
	get_minimum_delegation_return_data()
	}

Is that where you were thinking? Since Rust doesn't allow function overloading, is there a way we've handled similar conflicts in the past?

Also, I put the function in solana-stake-program because it is used in the implementation when the GetMinimumDelegation instruction is called/processed:

solana/programs/stake/src/stake_instruction.rs

Lines 402 to 413 in edf3f05

	Ok(StakeInstruction::GetMinimumDelegation) => {
	let feature_set = invoke_context.feature_set.as_ref();
	if !feature_set.is_active(
	&feature_set::add_get_minimum_delegation_instruction_to_stake_program::id(),
	) {
	// Retain previous behavior of always checking that the first account
	// is a stake account until the feature is activated
	let _ = get_stake_account()?;
	return Err(InstructionError::InvalidInstructionData);
	}
	let minimum_delegation = crate::get_minimum_delegation(feature_set);

Is it still best to move the fn?

[mvines]

Ah, I see.

My initial comment was made from the perspective of an off-chain user who's looking through RpcClient, such as the solana-cli.

They don't really have a nice way to determine the minimum delegation currently -- downside of our decision to not use a Sysvar. Their current choices seem to be:

1. Hardcode a value
2. Try to create the stake account with whatever stake amount the user provided, and attempt to gracefully handle the error from transaction simulation (or worse case, see the transaction fail)
3. Simulate a transaction with StakeInstruction::GetMinimumDelegation in it to retrieve the current minimum

[brooksprumo]

I was wondering if I should add a command to the CLI to get the stake minimum delegation. Would that be useful in this case?

[mvines]

An RpcClient method that does this would certainly be useful to the cli internally, so we can add the appropriate error handling when the user tries to create a new stake or split a stake with less than the minimum (ie, choice 3!)

[CriesofCarrots]

How about an RpcClient helper under the hood that performs simulate_transaction and returns parsed return_data of type T? I think we're going to want something similar for spl_token::instruction::GetAccountDataSize