Select with required attribute incorrectly reports missing value until value change occurs

[m-akinc]

🐛 Bug Report

Form validation on a select with required incorrectly reports a missing value until a value change has occurred. I.e. the initial value is not seen.

💁 Possible Solution

This happens because we try to mirror the initial value to the proxy native select element (within a call to super.slottedOptionsChanged()) before we have mirrored the child option elements. The native select will reject/ignore setting value if it doesn't correspond to the value of one of its child options (of which it has none, at that point). Right after mirroring the child options, there is a call to updateValue(), but because the value has already been updated earlier, it short-circuits, skipping the code path that would have updated the proxy.