Modifications to std::io::Stdin on Windows so that there is no longer a 4-byte buffer minimum in read().

[Patrick-Poitras]

This is an attempted fix of issue #91722, where a too-small buffer was passed to the read function of stdio on Windows. This caused an error to be returned when read_to_end or read_to_string were called. Both delegate to std::io::default_read_to_end, which creates a buffer that is of length >0, and forwards it to std::io::Stdin::read(). The latter method returns an error if the length of the buffer is less than 4, as there might not be enough space to allocate a UTF-16 character. This creates a problem when the buffer length is in 0 < N < 4, causing the bug.

The current modification creates an internal buffer, much like the one used for the write functions

I'd also like to acknowledge the help of @agausmann and @hkratz in detecting and isolating the bug, and for suggestions that made the fix possible.

Couple disclaimers:

• Firstly, I didn't know where to put code to replicate the bug found in the issue. It would probably be wise to add that case to the testing suite, but I'm afraid that I don't know where that test should be added.
• Secondly, the code is fairly fundamental to IO operations, so my fears are that this may cause some undesired side effects or performance loss in benchmarks. The testing suite runs on my computer, and it does fix the issue noted in read_to_end / read_to_string returns Invalid Input ("buffer too small") on Windows MSVC #91722.
• Thirdly, I left the "surrogate" field in the Stdin struct, but from a cursory glance, it seems to be serving the same purpose for other functions. Perhaps merging the two would be appropriate.

Finally, this is my first pull request to the rust language, and as such some things may be weird/unidiomatic/plain out bad. If there are any obvious improvements I could do to the code, or any other suggestions, I would appreciate them.

Edit: Closes #91722