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* [skip changelog] Bring shell scripts into compliance with standard formatting

A standardized style for all Arduino Tooling shell scripts has been established. The `.editorconfig` file is updated
accordingly and all the repository's scripts made compliant with it.

* [skip changelog] Sync install script with template

We have assembled a collection of reusable project assets:
https://github.com/arduino/tooling-project-assets
These assets will be used in the repositories of all Arduino tooling projects.

Some minor improvements and standardizations have been made in the upstream "template" installation script, and those are
introduced to this repository via this pull request.

Notable:

- ShellCheck compliance
- Support for specifying nightly build versions (e.g., "nightly-latest") via the script argument
- Remove cryptic output not of interest to the user (likely forgotten debug artifacts from script development)