Remove prefer_relative_imports and use absolute package imports

[ben-xD]

In analysis_options.yaml, we have

    # personal preference this conflicts with prefer_relative_imports
    # - always_use_package_imports

and

prefer_relative_imports # personal preference

• This reduces developer experience, because the IDE plugin (Flutter-Intellij, which is used in Android Studio too) auto-imports using absolute package paths, not relative paths. This rule goes against the default, and reduces efficiency with development because they have to explicitly fix the imports to be relative again: annoying/ waste of time. Therefore, it's not really personal preference.
• Current problem: Because of the plugin, these imports are already inconsistent. Some imports are relative, some are absolute, because again, the IDE automatically creates absolute ones.

TLDR: In this issue, we should remove the above code snippets, opting for always_use_package_imports instead. Then, we would update the paths. This would allow new developers to be productive and avoid linter warnings when auto importing anything.

┆Issue is synchronized with this Jira Story by Unito