fix(build): Remove node code from CDN bundles

[lobsterkatie]

This PR changes the way we substitute true for __SENTRY_BROWSER_BUNDLE__, the flag which enables us to treeshake anything Node-related out of CDN bundles.

There are two main changes:

• In the browser rollup config, the substitution is moved from the terser stage to an earlier stage, immediately after TS compilation, in order that the treeshaking we need now applies to all versions of the bundle, rather than just the minified ones.

• The substitution is added to all other rollup configs. (Even though packages like @sentry/tracing and @sentry/integrations are cross-platform, in this case we know we're building CDN bundles (which are only relevant in a browser setting), so it's safe to restrict it.)

As an example, here's the effect of these changes on the main browser bundle:

[github-actions]

size-limit report

Path	Base Size (4ff68c1)	Current Size	Change
@sentry/browser - ES5 CDN Bundle (gzipped + minified)	19.73 KB	19.72 KB	-0.03% 🔽
@sentry/browser - ES5 CDN Bundle (minified)	63.06 KB	63.04 KB	-0.04% 🔽
@sentry/browser - ES6 CDN Bundle (gzipped + minified)	18.44 KB	18.44 KB	+0.02% 🔺
@sentry/browser - ES6 CDN Bundle (minified)	56.5 KB	56.49 KB	-0.03% 🔽
@sentry/browser - Webpack (gzipped + minified)	22.16 KB	22.16 KB	0%
@sentry/browser - Webpack (minified)	75.87 KB	75.87 KB	0%
@sentry/react - Webpack (gzipped + minified)	22.19 KB	22.19 KB	0%
@sentry/nextjs Client - Webpack (gzipped + minified)	46.27 KB	46.27 KB	0%
@sentry/browser + @sentry/tracing - ES5 CDN Bundle (gzipped + minified)	28.3 KB	27.19 KB	-3.9% 🔽