Add Github actions support for library CI testing

[mikee47]

This PR adds a re-usable library workflow for Github actions so that Sming libraries can be independently tested.
It also tidies up the main ci.yml file and fixes a couple of minor related issues.

The library.yml re-useable workflow is provided, which takes care of these tasks:

• Checking in the library to test
• Checking in the Sming framework
• Installing build tools
• Builds all applications within the library's samples directory, for all supported architectures
• If a test application is provided then that should be located in a test directory.
  This is built for all architectures, and also executed for Host.

Builds are handled using :source:Tools/ci/library/Makefile.

See also https://docs.github.com/en/actions/using-workflows/reusing-workflows.

To use this in a project, add a suitable workflow to the .github/workflows directory. Templates are provided in the .github/workflows/library directory.

Here is the basic push scenario:

name: CI Push
on: [push]
jobs:
  build:
  uses: SmingHub/Sming/.github/workflows/library.yml@develop
  # Inputs are all optional, defaults are shown
  with:
    # Repository to fetch Sming from
    sming_repo: 'https://github.com/SmingHub/Sming'
    # Sming branch to run against
    sming_branch: 'develop'
    # Library alias
    alias: ''

The sming_repo and sming_branch inputs are provided if your library requires modifications to Sming which are not (yet) in the main repository.

The alias input is required where the library repository name does not correspond with the working title. For example, the jerryscript library is in a repository called Sming-jerryscript, so must be checked out using a different name. If Sming contains a library (or Component) with the same name then it will be overridden,
with a warning Multiple matches found for Component 'jerryscript' in the build log.

The ci-dispatch.yml example demonstrates manual triggering, which allows these inputs to be easily changed. See https://docs.github.com/en/actions/managing-workflow-runs/manually-running-a-workflow.

Note that the workflow must be available in the library's default branch, or it will not appear in the github web page.

[mikee47]

NB. This won't work of course until added to Sming repo. See https://github.com/mikee47/Sming-jerryscript/actions/runs/3350862770 for test run.