fixes #61126

Adds a new setting: `terminal.integrated.splitCwd`
With these options: `workspaceRoot`, `sourceInitialCwd`, `sourceCwd`
`workspaceRoot`is the existing behavior. The new split terminal's cwd will be the workspace root.
`sourceInitialCwd` uses the 'parent' terminals initial cwd for the new terminal.
`sourceCwd` on macOS and Linux this gets the cwd of the 'parent' terminal and uses that as the cwd for the new split terminal.
Default setting is to keep the existing behavior with `workspaceRoot`
Fixes #48447

Accounce terminal number every time the terminal is focused.

Fixes #52304

Fixes #60907

Using an overload makes the code more complex and prevents  patterns such as `.then(coalesce)` or `.map(coalesce)`. It also makes it clear which code paths are actually being most used in our code

#60656

#60656

#60565

Rewording / copy change

This reverts commit dbdbbe52.

Fixes #60806

Part of #60565

also use $mid as version id and only accept external and fsPath from the most recent version, #60163