Add a calculator to the ui vm

[brianmcgillion]

The calculator is a basic app with no network requirements so adding it
to the ui vm will just make it commonly available.

The venerable gnome-calculator is the best simple calculator from the
range of calculators that have been tested. It allows for both basic
calculator view with a history of the calculations and it also offers
modes for advanced and programming modes.

As such it should cover all cases although it is still quite a plain
looking app it is powerful and useful.

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Description of changes

Added the calculator app. It is accessible from the launcher and does what you would expect from a calculator.

Checklist for things done

• Summary of the proposed changes in the PR description
• More detailed description in the commit message(s)
• Commits are squashed into relevant entities - avoid a lot of minimal dev time commits in the PR
• Contribution guidelines followed
• Ghaf documentation updated with the commit - https://tiiuae.github.io/ghaf/
• PR linked to architecture documentation and requirement(s) (ticket id)
• Test procedure described (or includes tests). Select one or more:
  • Tested on Lenovo X1 x86_64
  • Tested on Jetson Orin NX or AGX aarch64
  • Tested on Polarfire riscv64
• Author has run make-checks and it passes
• All automatic Github Action checks pass - see actions
• Author has added reviewers and removed PR draft status
• Change requires full re-installation
• Change can be updated with nixos-rebuild ... switch

Instructions for Testing

• List all targets that this applies to:

• Is this a new feature

  • List the test steps to verify:
    open the app and do some math :)
    not much else to describe in the way of things to test

• If it is an improvement how does it impact existing functionality?

[barnabakos]

1 commit: c3b63d5
rebased to current tip of Ghaf main without conflicts: eb760c7

platform: Lenovo X1 Carbon; flash script

• ci-test-automation suite: ok
• starting apps: ok
• regression / ad-hoc testing: ok

works:

• basic math calculates
• math part of the app was not questioned during testing

notes:

• select "keyboard" & "currency":
  does not work; looks like an application issue
  hmmm, does it need network connection?
• looks like an unfinished software, major parts are working;
  currency converter most likely needs network and does not work