src/vs/editor/common/model/bracketPairsTextModelPart/bracketPairsTree/ast.ts/PairAstNode/create
class PairAstNode:	public static create(
		openingBracket: BracketAstNode,
		child: AstNode | null,
		closingBracket: BracketAstNode | null
	) {
		let length = openingBracket.length;
		if (child) {
			length = lengthAdd(length, child.length);
		}
		if (closingBracket) {
			length = lengthAdd(length, closingBracket.length);
		}
		return new PairAstNode(length, openingBracket, child, closingBracket, child ? child.missingOpeningBracketIds : SmallImmutableSet.getEmpty());
	}