chore(webapis): add tool for scanning for uses of Web APIs

[tido64]

Description

Implemented a tool for scanning for uses of Web APIs.

Test plan

1. Install Rust
2. Build and run:

   cd incubator/@react-native-webapis/scan
   cargo build -r
   cd ../../..
   ./incubator/@react-native-webapis/scan/target/release/scan

[kelset]

thanks for working on this!

I love that by going down the Rust route, the tool is blazing fast ⚡️

I left a few comment; aside from those, can we add a README.md to the root of scan that explains:

1. how to use it/build it
2. what the merge.mjs file is
3. what is the counting logic (if I read correctly, we count all instances across all files we find minus the ones in the ignored_dirs?)

[kelset]

thanks for addressing the feedback!