UiaElement copy ctor and assignment operator do subtly different things

[mlalic]

In the following snippet...

void Fn(UiaElement original)
{
  UiaElement newElement = original;
}

The newElement will end up aliasing the same remote object. More precisely, it'll refer to the same operand register as original (on the lowest-level of Remote Ops bytecode).

Meanwhile, in the following...

void Fn(UiaElement original)
{
  UiaElement newElement{ nullptr };
  newElement = original;
}

A Set instruction is emitted in the bytecode that assigns the original element to a new operand register in the bytecode.

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This means that two things that typically should work the same (the copy ctor and assignment operator) end up with subtly different behavior.

This issue tracks making a decision about this -- whether to try to make any changes to make these two operations work the same way or whether to document this rough edge as expected/by design.

[mlalic]

In a way this is related to #6 -- except for ints the current behavior seems obviously broken. Perhaps that should be an indication that we should make a fix across the board where copy ctors just do the same thing as assignment operators.