Fix TAC function parameter names

[alkorang]

This pull request fixes the issue that clients/visualizeout.py emits function parameter names different from variable names used in the function body.

For example, here is the decompiled contract.tac of examples/long_running.hex.

function 0x757(0x757arg0x0, 0x757arg0x1) private {
    ...
    0x76b: MSTORE v767(0x0), v757arg0
    ...
    0x7ea: RETURNPRIVATE v757arg1, v7e4_2
    ...
}

Function parameter names in the declaration are 0x757arg0x0, 0x757arg0x1, while they are v757arg0, v757arg1 in the function body.

This was because clients/visualizeout.py called the render_var function for variable definitions and variable uses in the function body, but not for function parameters. This PR fixes the issue by calling render_var for function.formals, too.

function 0x757(v757arg0, v757arg1) private {
    ...
    0x76b: MSTORE v767(0x0), v757arg0
    ...
    0x7ea: RETURNPRIVATE v757arg1, v7e4_2
    ...
}

[sifislag]

Thanks!