Fix incorrect temporary variable type in NewArray operation

[Troublor]

Fix #1776

When setting the type of the temporary variable from NewArray expression, the original code directly use the array base type instead of the array type.
This PR re-construct the ArrayType using the base type and the depth at L792-797 of file slither/slithir/convert.py.

One imperfect point is that length of nested array is lost since it is not stored in the NewArray expression, in other words, new uint[10][](2); expression will become new uint[][](2).
Fixing this will result in a great modification in the NewArray class, which may induce breaking change. So, I just leave it for future work.

[0xalpharush]

Thanks for identifying this issue! While it's reasonable to make incremental changes, it may be possible to fix this in one go. I haven't tested it a ton but I think something like this branch would simplify the code and make the IR more accurate. If you'd like to work off of it and add additional tests like for the case you mention (new uint[10][](2);), I'll assign the issue to you. I think the array string functions don't handle nested arrays properly when displaying it fwiw.

[Troublor]

@0xalpharush Sure. I would like to work on that enhancement. Please assign the issue to me.

[Troublor]

Closed in favor of #1784