Code Quality: Added a static method to the PCWSTR struct that allows constructing from a string

[Lamparter]

Resolved / Related Issues

• Related Code Quality: Replace Vanara with CsWin32 #15000

Steps used to test these changes

1. Built the app

This only introduces a new API that can be used in future PRs to make migrating from DllImport calls to CsWin32 generations easier, and does not have any effect over the app as it is.

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This method makes it easier to pass in a PCWSTR struct to a P/Invoke method that might previously require a string input.
A lot of methods generated by CsWin32 that require unsafe will prefer a PCWSTR passed as an argument over a literal System.String however this method allows using a string value (via fixing the string in memory as a char*) for simplicity and so that code isn't reused.

e.g.:

unsafe void Example()
{
	HANDLE file = PInvoke.CreateFile(lpFileName: PCWSTR.FromString("example") ...);
}

[0x5bfa]

This can cause memory corruption and thats why CsWin32 doesn't provide something like this.

[Lamparter]

This can cause memory corruption and thats why CsWin32 doesn't provide something like this.

@0x5bfa how do you propose that the PCWSTR struct is created from a managed string value then?