perf: cache UIFont construction based on FontDescriptor

[rigor789]

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What is the current behavior?

a new UIFont is constructed whenever a view is instantiated (that displays text).

What is the new behavior?

a new UIFont is created only when necessary, otherwise a single UIFont instance is reused.

Fixes/Implements/Closes #[Issue Number].

[rigor789]

The cache key generation is based on this benchmark (run in v8 based browser like chrome to get accurate results):

Benchmark