test-explorer: integrate `--strace`

[xhd2015]

Current test explorer UI includes Test & Debug functionalities, PR #213 introduced dynamic sub tests, making it easier and more funny to use.

The next step is to integrate with --strace, make it even more powerful.

This issue will trace related technical design and user experience considerations.

[xhd2015]

General desgin:

• add --strace-dir DIR , which if set will redirect the output to the target directory
• add a checkbox to toggle trace flag when running or debugging individual test
• if the trace is toggled on, show it after the test output. It can be viewed by scrolling down

[xhd2015]

Update: