Implement integrated terminal extension API

[Tyriar]

Fixes #9957

A demonstration of the API is available at https://github.com/Tyriar/vscode-terminal-api-example

[coveralls]

Coverage increased (+0.004%) to 62.538% when pulling ff87ab3 on tyriar/terminal_api into 9961aa2 on master.

[Tyriar]

@jrieken could you please take a look and see if everything looks fine?

[coveralls]

Coverage decreased (-2.2%) to 60.327% when pulling 2c95aed on tyriar/terminal_api into 9961aa2 on master.

[jrieken]

Is this always the same sequence for new line or should addNewLine be something like \n|\r\n|\r?

[jrieken]

missing return type, comment for text

[coveralls]

Coverage decreased (-2.2%) to 60.327% when pulling d3dd3c6 on tyriar/terminal_api into 9961aa2 on master.

[coveralls]

Coverage decreased (-2.2%) to 60.342% when pulling 2fb2d9a on tyriar/terminal_api into 9961aa2 on master.

[Tyriar]

Merging but reopening the issue until Terminal.hide() hides the current terminal, not just the panel regardless of which terminal is active.

[guogaigai]

Is there any terminal API provided for extension developers to create a terminal with the specified path as the initially start ,thank you @Tyriar

[Tyriar]

@guogaigai please just file an issue next time instead of commenting on several issues. This is a good request, I created #10917

[guogaigai]

thank you very much @Tyriar