Public properties with duplicate getter/setter should be an error

[nolanlawson]

In #2501, we had to revert an unintended breaking change due to duplicate getter/setters. For instance:

export default class Text {
    @api foo = 1;
    
    get foo() {}
    set foo(value) {}
}

This is clearly a mistake, and should be treated as an error (ideally by the compiler). But today, we are allowing this syntax, to preserve backwards compatibility:

lwc/packages/@lwc/engine-core/src/framework/decorators/register.ts

Lines 218 to 225 in d004e93

	// [W-9927596] If a component has both a public property and a private setter/getter
	// with the same name, the property is defined as a public accessor. This branch is
	// only here for backward compatibility reasons.
	if (!isUndefined(descriptor) && !isUndefined(descriptor.get)) {
	descriptor = createPublicAccessorDescriptor(fieldName, descriptor);
	} else {
	descriptor = createPublicPropertyDescriptor(fieldName);
	}