Handle out-of-order binding of identifiers to improve tree-shaking

[lukastaegert]

This PR contains:

• bugfix
• feature
• refactor
• documentation
• other

Are tests included?

• yes (bugfixes and features will not be merged without tests)
• no

Breaking Changes?

• yes (breaking changes will not be merged unless absolutely necessary)
• no

List any relevant issue numbers:
Resolves #2799

Description

It is possible that Rollup needs to analyze values of identifiers before they have been bound to their variables, which can cause in sub-optimal tree-shaking results. This is fixed here by allowing out-of-order binding of identifiers if their value is needed earlier. This allows for the following:

// input
export const test = () => {
	console.log(foo());
	console.log(bar());
};

const foo = () => {
	return BUILD ? A : B;
};

const bar = () => {
	return getBuild() ? A : B;
};

const getBuild = () => BUILD;

const BUILD = true;

// output
const test = () => {
	console.log(foo());
	console.log(bar());
};

const foo = () => {
	return A;
};

const bar = () => {
	return A;
};

export { test };