Migrate from fs4 to std::File flocks

[wmmc88]

From https://github.com/microsoft/windows-drivers-rs/pull/295/files#r1964235574. flocks are used in both wdk-macros and wdk-macro-tests.

This was stabilized in 1.87(released in may), so we'll have to wait until 1.88 to make this change (~june 26th)