Fix bug of fp16 converter about the cast node and topology in sub-graph

[xiaowuhu]

There have a lot of bugs in the float16 converter after ORT 1.17 released, because the optimization rule changed in ORT. And customers also raised a lot of fp16 converter issue, which to be considered as corner case, but also need to fix. The original implementation is hard to understand, less maintainable. So I rewrite the function convert_float_to_float16, the logic is simple to understand, and easy to modify each components. Also added 3 new features:

• remove identity node when it is unnecessary.
• remove cast node when it is unnecessary.
• sort topology if ORT complain the topology is not in order, the input of node 'x' is not output of any previous node.

[fatcat-z]

Please add some descriptions so we know what kind of issue this PR aims to address.