Integrated terminal should not be resused if a process is running in it

[a1994846931931]

Description

If a process is running in an integrated terminal, then a new integrated terminal should be provided for runInTerminal request. Otherwise, it could be problematic, even dangerous.

Reproduction Steps

In the demo above, if the terminal is already running python, sending command text to that terminal will end in chaos.

What's worse? Think about a situation where a user happens to be operating a database, e.g. MySQL, in the opened integrated terminal, it could be dangerous to send commands to that terminal!

Propose

1. Remove integrated terminals with any child process from for-reuse candidates
   I learned the logic from VSCode. Please refer to:
   https://github.com/microsoft/vscode/blob/4636be2b71c87bfb0bfe3c94278b447a5efcc1f1/src/vs/workbench/api/node/extHostDebugService.ts#L83-L87
   and
   https://github.com/microsoft/vscode/blob/4636be2b71c87bfb0bfe3c94278b447a5efcc1f1/src/vs/workbench/contrib/debug/node/terminals.ts#L50-L75

Demo from VSCode:

2. Don't change the title of the integrated terminal
   Compare the title of the integrated terminal of VSCode to theia:
   VSCode:
   
   Theia:
   

• In the case of theia, I believe it is hard for users to distinguish the special integrated terminals from the normal ones and they are more likely to run command in that terminal.
• In the case of VSCode, it's not hard to imagine that users will be aware of which ones are integrated terminal. And even if they mistakenly run a process in that terminal, which ends in prompting VSCode opening a new terminal, they are more likely to understand what's happening and avoid using that terminal the next time.

OS and Theia version:
OS: Linux
Theia: Latest(582ae9d)

Diagnostics:

[akosyakov]

@a1994846931931 PRs are welcomed.