[DRAFT] Implement manual liquidation path

[jordanschalm]

Closes: #???

Description

Implements a manual liquidation path. Anyone is allowed to perform a liquidation under the following circumstances:

• The position is unhealthy (H<1)
• The liquidation offer provides a better implied price for the seized collateral than the protocol could get from a DEX
• The liquidation offer does not cause the health to exceed target (1.05)
• The price provided by the DEX does not diverge too far from the price provided by the oracle

Notes for reviewers while in draft state

The skeleton of the implementation is largely complete, but this lacks tests, and proper documentation in some places.

• This PR introduces SwapperProvider to represent a DEX. We need to add an implementation of SwapperProvider that can be used.
• There are lots of TODO comments I left as I read through the code, of varying relevance to liquidation. I suggest focussing review on the new liquidation logic in manualLiquidation and _doLiquidation

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For contributor use:

• Targeted PR against master branch
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the standards mentioned here.
• Updated relevant documentation
• Re-reviewed Files changed in the Github PR explorer
• Added appropriate labels

[turbolent]

trueBalance always uses the snapshot's creditIndex. Should this use the debitIndex here?

[turbolent]

Here and below: FlowCreditMarketMath.one is deprecated, just use the literal:

Suggested change

	self.creditInterestIndex = FlowCreditMarketMath.one // TODO: hard-coded to 1?
	self.debitInterestIndex = FlowCreditMarketMath.one // TODO: hard-coded to 1?
	self.creditInterestIndex = 1.0
	self.debitInterestIndex = 1.0

[turbolent]

Suggested change

	let trueBalance = FlowCreditMarket.scaledBalanceToTrueBalance(
	balance.scaledBalance,
	interestIndex: tokenSnapshot.creditIndex
	)
	return trueBalance
	return FlowCreditMarket.scaledBalanceToTrueBalance(
	balance.scaledBalance,
	interestIndex: tokenSnapshot.creditIndex
	)

Also see below: Maybe there should be two functions, or make it more obvious in the function name that the creditIndex is used and not debitIndex