[New Feature] Multi-resolution screenshot generator

[kdmukai]

Overview

Adds support for generating screenshots beyond our original 240x240 resolution.

• Automatically adds all supported display resolutions found in SettingsConstants.
• Adds a --resolution command line option to render any new arbitrary resolution. Note that our baseline 240x240 resolution is always rendered, regardless of this option.
• Adds a --no-clean option to prevent wiping out the screenshots dir before generating.
• Minor refactor in generator.py to treat it as a class-based test case. This provides a clear universal setup/teardown, regardless of how many screenshot combinations (locale @ resolution) are generated.

Discussion items

• I needed to be able to track state in the screenshot generator across individual locale / resolution invocations within a given run. Now that it's been refactored into a class based test, I opted to use some slightly hack-y class-level attrs for that state management (locale_combos, have_cleaned_screenshots_dir). I can't decide if it's clever, ugly, or somewhere inbetween.

• Default behavior: clean the screenshots dir. Many times in the past I've been confused by a screenshot that turned out to just be stale that wasn't part of the most recent run. But on the flip side, there have definitely been times when I found it convenient to keep prior screenshots around (e.g. screenshots for a new locale I'm testing), even if they did risk becoming a bit stale. So the --no-clean option gives us flexibility. But either way, the final README will only link up the screenshots from that particular run.

Future TODO items

• As we get deeper into supporting a wider variety of screens, it'll be easier to figure out how to clean up the slightly half-baked organizational overlap between SettingsConstants.ALL_DISPLAY_CONFIGURATIONS and the display_driver.ALL_DISPLAY_TYPES constants. It's currently a little redundant but it's not horrible enough to need refactoring right now.

• The final README hard codes four of the English 240x240 screenshots to enhance the README's presentation. But the --locale option plus the default dir clean means that those screenshots aren't guaranteed to exist. A future enhancement would be to make those preview embeds dynamic.

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This pull request is categorized as a:

• New feature

Checklist

• I’ve run pytest and made sure all unit tests pass before sumbitting the PR

If you modified or added functionality/workflow, did you add new unit tests?

• N/A

I have tested this PR on the following platforms/os:

• Other: screenshot generator is only meant to run in local dev