feat: add support for parsing Flow, applied to RN modules by default

[ambar]

Closes #3

Added two options:

• bundleSize.flowPattern: The regexp pattern to match files containing the Flow type
• bundleSize.loader: Override the loader in Bundle Size (eg: .js: jsx will force .js files to be treated as JSX), see esbuild#loader for more details

[coveralls]

Pull Request Test Coverage Report for Build 4bfd664c51c7e1f4a8ca5fcf95118f34b1927e46

• 0 of 12 (100.0%) changed or added relevant lines in 2 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage increased (+1.5%) to 90.887%

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Totals
Change from base Build 28baa009444f7d6cb1b030fb702358fbde12ead5:	1.5%
Covered Lines:	286
Relevant Lines:	299

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💛 - Coveralls