docs(dependency-injection): Clarify how TypeScript generates decorator metadata

[Igonato]

I think it's important to mention the compiler option. After reading the note I wanted to see how this magic works and what it looks like in a compiled javascript and tried to make a simple test in TypeScript playground. I got nothing and it took some time to figure out that a compiler option is involved in this.

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[Igonato]

I signed it!

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CLAs look good, thanks!

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CLAs look good, thanks!

[Foxandxss]

I like it.

[wardbell]

Thank you. I agree. I took the liberty of further clarifying this point.