Rollout for terminal env var activation

[cwebster-99]

• Add new experiment in the control tower @cwebster-99
• Rollout behavior for Insiders
• Rollout behavior in stable
• Address/Close out existing issues which are fixed by experiment
• 🏃Address new issues which come up (see PRs referencing this issue or VS Code issues relating to new terminal activation feature #22879)
• Make sure upstream issues on VS Code in Incorporate fixes from VSCode regarding Environment collection API #20822 are fixed
• Remove python.terminal.activateEnvInCurrentTerminal setting
• Move how Python environments activate docs to website vscode-docs#6590
• Push for VS Code issues relating to new terminal activation feature #22879

[karrtikr]

@cwebster-99 I have already added an experiment in control tower as part of my work, goes by the name "pythonTerminalEnvVarActivation".

[septatrix]

With this experiment active, activation fails for fish shells and I currently have to explicitly opt out.