Support JSON debugging output

[katat]

This PR added API getJSONOutput, which can search and parse signals based on object keyword, such as this test. Any symbol string matching the regex text will be parsed and organized as json output for testing assertions.

I was inspired to make this feature, as there seems no similar APIs to help the debug process. In debugging, if I wanted to look into the signal values, I have to manually parse the symbols and values and this is quite a cumbersome process especially when the size of circuit is big.

This would be particularly useful when the number of different signals is large as it helps navigate the debugging targets without costing too much overhead unnecessarily parsing all the signals for every test.