Fix rollup validate script

[koba04]

Summary

This reverts #18899 and re-enables #18897.
The issue is caused by eslint/eslint#12888 because ESLint v7 ignores node_modules/* in subdirectories.
To fix this, I've add !/build/node_modules/* into eslintignore for the rollup validate script.
I've tested this with yarn lint-build. Is there anything else I have to test?
Should I add a check to run yarn lint-build at every PRs?

Test Plan

yarn lint-build

➜  yarn lint-build
yarn run v1.22.4
$ node ./scripts/rollup/validate/index.js
Checking if files exist in ./build/react-native/implementations/*.js...
Found 12 bundles.

Checking if files exist in ./build/node_modules/*/umd/*.js...
Found 32 bundles.

Checking if files exist in ./build/node_modules/*/*.js...
Found 54 bundles.

Checking if files exist in ./build/node_modules/*/cjs/*.js...
Found 90 bundles.

Linting rn bundles...
Linted rn bundles successfully!

Linting umd bundles...
Linted umd bundles successfully!

Linting cjs bundles...
Linted cjs bundles successfully!

✨  Done in 12.83s.

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