Reuse internal Locale's cache instead of custom cache

[antagoony]

🤔 What's changed?

As a side-effect of your response within #376 I took a deeper look to all positions where the Locale information is stored. Doing so, I found a custom Locale cache even though the Locale class already provides an internal caching mechanism (Locale#LOCALECACHE). Admittedly, this cache will not be used when creating Locale instances by any of the Locale constructors. Instead, one must use the Locale.Builder.

This PR removes the custom Locale cache and reuses the Java built-in cache mechanism.

⚡️ What's your motivation?

I like the idea of having "a single source of truth", and this PR removes one of the code positions where the current Locale information is stored a second time.

🏷️ What kind of change is this?

• 🏦 Refactoring/debt/DX (improvement to code design, tooling, etc. without changing behaviour)

♻️ Anything particular you want feedback on?

No.

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct

[mpkorstanje]

Cheers!