Add-on store: Improve disk management for launcher and secure copies

[seanbudd]

Link to issue number:

Part of #13985
Originally raised by @XLTechie in #14912 (reply in thread)

Summary of the issue:

The installer for add-on store versions of NVDA, is creating the addonStore folder in %appdata%\nvda, even before the license agreement is accepted!
E.g. If starting the installer, and selecting "exit" instead of agreeing to the license agreement, the addonStore directory is created and populated with some files and directories under %appdata%\nvda.
It won't create %appdata%\nvda, but if that already exists, it will create the store directory.

This is absolutely not expected behavior. NVDA should never be doing any directory and file creation on the local system before "install" is selected.
I have not looked at the code, so do not know what this would do to an existing installed store copy, but really no user would expect that the installed NVDA's configuration could be altered by an installer that was not told to "install".

Description of user facing changes

Ensure the caching behaviour of add-ons matches that of NVDA's config.
Files should only be written to disk when not running as launcher nor in a secure context.

Description of development approach

Adds relevant checks to prevent saving the add-on handler state and add-on store caches to disk.

Testing strategy:

• Manual testing to be confirmed

Known issues with pull request:

None

Change log entries:

N/A

Code Review Checklist:

• Pull Request description:
  • description is up to date
  • change log entries
• Testing:
  • Unit tests
  • System (end to end) tests
  • Manual testing
• API is compatible with existing add-ons.
• Documentation:
  • User Documentation
  • Developer / Technical Documentation
  • Context sensitive help for GUI changes
• UX of all users considered:
  • Speech
  • Braille
  • Low Vision
  • Different web browsers
  • Localization in other languages / culture than English
• Security precautions taken.

[AppVeyorBot]

• PASS: Translation comments check.
• PASS: Unit tests.
• PASS: Lint check.
• FAIL: System tests (tags: installer NVDA). See test results for more information.
• Build (for testing PR): https://ci.appveyor.com/api/buildjobs/clpyh4g4bans6fo3/artifacts/output/nvda_snapshot_pr14955-28306,f87035a1.exe
• CI timing (mins):
  INIT 0.0,
  INSTALL_START 1.0,
  INSTALL_END 0.9,
  BUILD_START 0.0,
  BUILD_END 25.6,
  TESTSETUP_START 0.0,
  TESTSETUP_END 0.3,
  TEST_START 0.0,
  TEST_END 23.0,
  FINISH_END 0.1

See test results for failed build of commit f87035a14f

[XLTechie]

Thanks @seanbudd!