fix(42734): TS18030: An optional chain cannot contain private identifiers

[a-tarasyuk]

Fixes #42734

[dragomirtitian]

@a-tarasyuk I looked at this issue too but got stuck on emit changes. The private field transform will now just remove the ?. checks:

This:

class X {
    #test = 0;
    m() {
        let a: X | undefined = undefined;
        a?.#test
    }
}

Transforms to this:

class X {
    constructor() {
        _test.set(this, 0);
    }
    m() {
        let a = undefined;
        __classPrivateFieldGet(a, _test);
    }
}

which will result in a Type error.
Playground Link

[a-tarasyuk]

It looks like classFields doesn't support OptionalChain transformation.

TypeScript/src/compiler/transformers/classFields.ts

Lines 231 to 241 in 2a01f92

	function visitPropertyAccessExpression(node: PropertyAccessExpression) {
	if (shouldTransformPrivateFields && isPrivateIdentifier(node.name)) {
	const privateIdentifierInfo = accessPrivateIdentifier(node.name);
	if (privateIdentifierInfo) {
	return setOriginalNode(
	createPrivateIdentifierAccess(privateIdentifierInfo, node.expression),
	node
	);
	}
	}
	return visitEachChild(node, visitor, context);

@rbuckton Can we share OptionalChain transformation from es2020 with the classFields?