add experience part 1

[lstebner]

What this PR does

The goal of this PR is to lay some groundwork for an experience based level system as outlined in #371

• add 'experience' to farmhand state
• add 'useLegacyLevelingSystem' to farmhand state and settings screen (only shown when the EXPERIENCE feature is enabled)
• update levelAchieved to be more flexible about how level is calculated based on which leveling system is being used
• update all calls to levelAchieved
• update utils unit tests for levelAchieved to test both systems
• add 'EXPERIENCE' feature flag
• add reducer for adding experience + unit test
• some utils were moved into their own files to make them easier to work with (mostly to avoid circular dependencies when one util relies on another util) and imports across the codebase were updated
• initialize experience value to match number of items sold when loading a saved game
• add 1 experience point per farm item sold (crops, milks, and crafted or forged items)
• items that are not farm items should not reward the player with any experience (seeds, weeds, other supplies)
• importing a save without experience should calculate experience based on items sold

How this change can be validated

This PR would be easiest to test if checked out and ran locally so that the feature flag can be flipped on and off

With the feature flag enabled:

• [x] there should be a setting in the settings window to toggle between the legacy system and the new system
• [x] the use legacy setting should be persist

With the flag disabled:

• [x] the settings menu should not show the toggle for changing which leveling system is used

Regardless of flag enabled or disabled, these things should happen:

• [x] an experience value can be seen when inspecting the Farmhand root component
• [x] the experience value in state should match the total number of items sold when loading a saved game that previously did not have experience
• [x] experience should increment by 1 for each item sold

Questions or concerns about this change

Additional information

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Name	Status	Preview	Comments	Updated (UTC)
farmhand	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	Aug 30, 2023 5:10am

[lstebner]

thanks for calling those things out @jeremyckahn . i've made some updates now to handle importing saves and making sure that experience is only rewarded for farm products sold.