ti_Resize function that preserves file contents

[runer112]

I would expect ti_Resize to add/remove bytes at the current offset, or maybe at the end, but it instead appears to do so at the start of the file.

[mateoconlechuga]

ti_Resize was never intended to preserve file contents.

[adriweb]

Since we can't modify the function's behavior now anyway, the consensus on Discord was to create a new function that does this, if needed.

[mateoconlechuga]

Documentation added in 06c34a0 to note that this function doesn't preserve file contents