ref: Add no-class-field-initializers eslint rule

[mydea]

Adding a lint rule (see #5316) to enforce initializing of fields in constructor, to reduce bundle size of transpiled code (and streamline this a bit overall).

Closes #5316

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	74.69 KB (-0.55% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.1 KB (-0.97% 🔽)
@sentry/browser - Webpack (gzipped)	21.8 KB (-0.69% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	69.49 KB (-0.49% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	28.13 KB (-0.58% 🔽)
@sentry/browser - ES6 CDN Bundle (gzipped)	20.14 KB (-0.95% 🔽)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	218.86 KB (-0.99% 🔽)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	84.57 KB (-1.66% 🔽)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	59.74 KB (-1.23% 🔽)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	30.42 KB (+0.02% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	64.9 KB (-0.41% 🔽)
@sentry/react - Webpack (gzipped)	21.83 KB (-0.61% 🔽)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	92.51 KB (-0.45% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	50.62 KB (-0.55% 🔽)

[Lms24]

Nice! Solid size reduction!