fix: update path for schema

[zixiang2018]

Context

To resolve this error when npm i.

npm ERR! command failed
npm ERR! command sh -c node scripts/postInstall
npm ERR! node:internal/modules/cjs/loader:1078
npm ERR!   throw err;
npm ERR!   ^
npm ERR! 
npm ERR! Error: Cannot find module '../src/2.0/schema/schema.json'

What this PR does

• follow the quicktype command in postInstall which uses process.cwd to check for current working directory
• remove schema compilation logic from postInstall.js so that npm i wont trigger it. Furthermore, made use of prebuild script (preBuild.js) to compile schema
• add prebuild script in test so that test files can retrieve the schema files

[HJunyuan]

Just to be clear, prebuild should automatically run when npm run build is triggered. But since we don't build before running our tests, I understand we have to manually call it here

[zixiang2018]

Yup! Didnt wanted to add a npm run build in here because its not needed by the test script

[github-actions]

🎉 This PR is included in version 6.9.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• GitHub release

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