Add prompts when installer aborts terminal or needs install location

[florelis]

Resolves: #713
Resolves: #970

Changes:

• Added user setting for default install root
• Added prompts when an installer has InstallerAbortsTerminal (to confirm that we want to install) or InstallLocationRequired (to provide the install location).
• Refactored the existing package agreements prompt to a common setup also used by the two new prompts. Before installing a package, we walk through all the possible prompts and show them if applicable. When installing multiple packages, we check all the packages that need the prompt and then show the prompt once.

Remaining items:

• Testing
• Use install root from settings
• Update settings doc
• Move installers that abort the terminal to the end on upgrade all/import
• Skip prompts when running non-interactively

Microsoft Reviewers: Open in CodeFlow

[JohnMcPMS]

My comments on the default install root setting also apply to the install location argument on a multipackage install. I'm just not sure it makes sense to have one location apply to multiple packages.

[florelis]

Note that this is still missing tests, validation of the install root and the arg/setting to disable prompts. (Hence still a draft)

I had thought of moving installers that abort the terminal to the end so as to minimize their impact, but that seems tricky with dependencies.

[florelis]

Reviving this old PR...

Main changes from last time:

• Rebased on recent main branch
• Added a setting and a CLI arg to prevent all prompts
• Added unit tests

[florelis]

This PR is having issues with the COM InProc E2E tests because I added something that causes us to load the string resources in a place we weren't doing it before, and the tests fail there because they cannot find the resources. I still don't know how to fix it (and it would make this change bigger), so I'm sidestepping it for now by preventing this new use of the ResourceLoader. I'll open an issue for actually fixing it because I imagine it will hit us again later.