[3.x] Allow RationalMoney instances as base price

[voidgraphics]

Almost all of the \Brick\Money\Money typehints have been replaced with \Brick\Money\AbstractMoney, so that instances of \Brick\Money\RationalMoney can also be used as a base for Price instances.

This is necessary when doing operations without rounding in order to avoid errors in the end result.

An example of the problem:

We have a base price of 1000 minor units, that we need to divide by 12 and then multiply by 11.

1000 / 12 * 11 = 916,6666666667

Using the regular Brick\Money\Money class forces us to specify a rounding mode when doing the division, which means we have a rounded result before doing the multiplication, which introduces an error in the result:

The solution is to build the Price instance with a base Brick\Money\RationalMoney instance instead, which represents the amount as a fraction and thus does not require rounding.

Unfortunately, the change to AbstractMoney typehints in the Whitecube\Price\PriceAmendable interface is a breaking change, so this requires publishing a new major version of this package (3.x ?).

My changes in this PR are quite conservative, they require the developer to pay attention to what they are doing and puts the responsibility on them to know when they will need to use RationalMoney instead of regular Money instances.

I think this is dangerous. Maybe this package should instead always use RationalMoney under the hood, so that division/multiplication is always handled correctly. I don't think there would be any downsides to that approach.

[toonvandenbos]

Maybe this package should instead always use RationalMoney under the hood, so that division/multiplication is always handled correctly.

Good point. I'll need to check the implications first.

[voidgraphics]

Tests fail on PHP 7.4 because of the static return type.

[toonvandenbos]

Remove use statement if unused?

[voidgraphics]

Used on lines 114 & 131

[toonvandenbos]

Remove unused use statements.

[voidgraphics]

Used on lines 110, 118, 124 & 128

[toonvandenbos]

Missing types for $perUnit & $postVat

[toonvandenbos]

$formatter can be string, callable or CustomFormatter, which could be specified for IDE users instead of mixed.

Suggested change

	static public function formatUsing(mixed $formatter): CustomFormatter
	static public function formatUsing(string|callable|CustomFormatter $formatter): CustomFormatter

[toonvandenbos]

$modifier can either be string, callable, AbstractMoney , Price or PriceAmendable

Suggested change

	protected function makeModifier(string $type, mixed $modifier, array $arguments = []): PriceAmendable
	protected function makeModifier(string $type, string|callable|AbstractMoney|Price|PriceAmendable $modifier, array $arguments = []): PriceAmendable

[toonvandenbos]

Suggested change

	public function addModifier(string $type, mixed $modifier, ...$arguments): static
	public function addModifier(string $type, string|callable|AbstractMoney|Price|PriceAmendable $modifier, ...$arguments): static

[toonvandenbos]

Suggested change

	public function addDiscount(mixed $modifier, ...$arguments): static
	public function addDiscount(string|callable|AbstractMoney|Price|PriceAmendable $modifier, ...$arguments): static

[toonvandenbos]

Suggested change

	public function addTax(mixed $modifier, ...$arguments): static
	public function addTax(string|callable|AbstractMoney|Price|PriceAmendable $modifier, ...$arguments): static

[toonvandenbos]

(Not sure about this one)

Suggested change

	public function setUnits(mixed $value): static
	public function setUnits(float|int|string $value): static

[toonvandenbos]

... and so on. Same remarks can be applied everywhere.