Part of #78168

Fixes #78540

* Adopt TerminalVirtualProcess for Custom task execution

* Update Custom task execution API to return TerminalVirtualProcess in callback

This also required the addtion of a start on the virtual terminal process

* Clarify start API

Fixes #76492

* Adding support for TaskProvider.resolveTask.

* Reorganize task grouping and resolution async code for readability.

* Made small changes and implmented resolveTask for gulp

Fixes #58718

Fixes #73412

Add a presentaion option for tasks to automatically show the problems panel.
Fixes #44146

Fixes #71179

Not sure why this wasn't a compile error

Fixes #70958

Fixes #67463

#70352

Fixes #70511

Fixes #69685

Clean up comments, fix some code review issues, and make the exit code optional throughout to make it clear that it isn't always a number

Fixes #68411

Fixes #66561

* Return splitted instance from ITerminalService::splitInstance

* Add support for terminalGroup to tasks

* Early-exit when the tab could not be split

https://github.com/Microsoft/vscode/pull/65973/files/42e3171a71ae4b6963e47318fd289a66eb48a96a#r245762395

* Use .get()! instead of the unsupported [] to access LinkedMap

* Move api changes into `vscode.proposed.d.ts`

* Rename "terminalGroup" to "group"

* Only keep references to terminals in sameTaskTerminals and idleTaskTerminals if the terminal is not disposed

* Type result variable

Fixes #47265

Part of #63453

Part of #63453

Fixes #64166

Use `Array<T | U>` when dealing with union types instead of  `(T | U)[]`

Fixes #64040

Fixes #62789

Fixes #17147