Make sure zero bytes are not discarded when converting strings

[spahnke]

Since C++ uses zero byte terminated strings, a cast to wchar_t* discards all characters after a zero byte when used directly to create a C# or V8 string. This is bad for strings containing a zero byte somewhere. We fix that by using a constructor overload taking the actual length of the string as parameter.

Example:

const text = 'a\0b'
text

would arrive as "a" in C# without the fix and vice versa.

[Ablu]

a cast to wchar_t* discards all characters after a zero byte

Not the cast discards it, but the String constructor without length parameter :)

EDIT: Ok, the comment in the code is right, just the PR description was slightly misleading.