Implement terminal shell integration

[Tyriar]

Shell integration involves injecting sequences into the prompt such that we know additional information about what is happening in the process such as:

• The start of the prompt
• The end of the prompt/start of the input
• The end of the input
• The current working directory
• The exit code of last process/command

This additional information enables a lot of possibilities:

• A more reliable and faster mechanism for detecting the cwd - one that actually works on Windows (at least for pwsh). For Windows this would allow lighting up some functionality that's currently disabled like inheriting the cwd in split terminals or resolving links relative to the cwd.
• Track command prompts, inputs and their output. This enables things like tracking command history, separating "execution blocks", collapsing past output, block-level actions/context menu, etc.
• Potentially exposing a run command extension API which runs within an existing shell session and returns the exit code, additional state could also be exposed via Terminal.state.
• Overall better awareness of what's going on inside the terminal, currently it's mostly a black box and the main ways of detecting things is via scanning all text (eg. tasks) or by listening for certain key presses (eg. current command tracking).
• If we know reliably when input is being accepted into the shell and what the current input is, we could provide auto-complete of history - this could even be extended to extensions in a similar way that the text area does it. Taking this a step further, monaco could potentially be used which enabled multi-cursor, familiar shortcuts, etc. (that would lose native shell autocomplete though).

Notes:

• This needs to be implemented on a per-shell basis
• We're adding the ability to indicate "process capabilities" in Polish when cwdFolder is shown in terminal description and add ProcessCapabilities #133037, this could be used to take a progressive enhancement approach by lighting up functionality when it's available
• The shell integration itself could be implemented either by instructing the user to amend their profile script or by exposing a new builtin terminal profile
• Powershell on Windows support seems to be possible
• For full Windows support on conpty, detecting the start of input positioning would need OSC sequences in prompt get front loaded terminal#11220 (Conpty "pass-through" doesn't maintain order of operations terminal#8698)