Replace implicit conversions in UiaOperationAbstraction with explicit ones

[beweedon]

Types in UiaOperationAbstraction can often be converted to their local and remote variants implicitly. For example, passing a UiaString to a function that takes a wil::shared_bstr will perform the conversion automatically due to the UiaString method operator wil::shared_bstr() const;. These conversions throw if you try to convert a remote abstraction instance into its local variant, or a local abstraction instance into its remote variant. This can result in accidental and often confusing bugs.

It's worth having discussion on whether we want to move towards more explicit conversions to avoid these subtle bugs. This would be a breaking change for UiaOperationAbstraction consumers.

[beweedon]

@michaelDCurran @zhayuli

[ggordon-vispero]

I actually like the implicit conversions but understand the counter arguments. Could the conversions all be placed in one of the headers, if they aren't already, and surrounded with ifdefs? I've not looked at the code recently enough to know if this could also be dealt with by putting the conversions in their own namespace which the client could "use" if they're wanted.