Manually pre-evaluate the starting directory when calling elevate-shim

[zadjii-msft]

targets #15280

When ctrl+clicking on a profile, pre-evaluate the starting directory of that profile, and stash that in the commandline we pass to elevate shim.

So in the case of something like "use parent process directory", we'll run elevate-shim new-tab -p {guid} -d "C:\\the path\\of\\terminal\\."

Closes #15173

[zadjii-msft]

230be3e fixed the earlier issue I saw, where a profile that wasn't a relative path would actually just open in the vcwd. Now this branch works too.

[lhecker]

winrt::hstring is implicitly convertible to std::wstring_view, so there's no need for explicit casts like this most of the time. It just doesn't work for something like std::filesystem::path::operator/=, because C++ wouldn't know which of the 31 overloads to call, given a hstring.

Also, when cppwinrt generates String parameters for functions, it'll not use winrt::hstring but winrt::param::hstring which binds to almost any string type, include std::wstring, without making any extra copies on the heap. We can thus just return a std::wstring from this function and it'll work without any additional modifications.