refactor(langauge-core): codegen based on Generator

[johnsoncodehk]

To reduce codegen function context, for past code:

function generateScript() {

	const codes = [];

	return codes;

	function generateSrc() {
		codes.push(...);
	}
	function generateHelperTypes() {
		codes.push(...);
	}
}

It should refactor to:

function generateScript() {

	yield* generateSrc();
	yield* generateHelperTypes();

	function generateSrc() {
		yield ...;
	}
	function generateHelperTypes() {
		yield ...;
	}
}

And codegen should be able to split into smaller files more easily in the future.