Multiple Extensions for a View Engine

[ItzNotABug]

A view engine can support multiple file types, example -

1. HBS View Engine supports .hbs & .html files
2. JSX View Engine supports .js, .jsx & .tsx files

Current implementations requires adding an engine for each extension which can be repetitive, this PR addresses that issue.

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Previously -

express.engine('js', jsx.engine);
express.engine('jsx', jsx.engine);
express.engine('tsx', jsx.engine);

New Approach -

express.engine(['js', 'jsx', 'tsx'], jsx.engine);