[SDK][Experiments] Remove bundled core-js polyfills and reduce consumer bundle size

Description

The published @dotcms/experiments package is a single large module exporting only withExperiments.

Current artifact observations:

• core-web/dist/libs/sdk/experiments/index.esm.js: approximately 256 KB raw.
• An isolated minified consumer import measured approximately 108 KB raw / 41.5 KB gzip.
• The artifact contains many core-js fingerprints and global-patching code alongside the experiments/Jitsu implementation.

Because the package exposes one feature from one flat module, consumers cannot tree-shake the internal implementation. More importantly, adding sideEffects: false now may be unsafe: the bundled compatibility code appears to modify globals during module evaluation.

Relevant files:

• core-web/libs/sdk/experiments/src/index.ts
• core-web/libs/sdk/experiments/src/lib/components/withExperiments.tsx
• core-web/libs/sdk/experiments/src/lib/dot-experiments.ts
• core-web/libs/sdk/experiments/rollup.config.cjs
• core-web/dist/libs/sdk/experiments/index.esm.js

Determine whether core-js is introduced by Jitsu, Babel/Rollup configuration, or another build-stage dependency. Remove the inlined polyfills rather than hiding them with side-effect metadata. Consider externalizing or lazily importing the analytics transport after the source is confirmed.

Acceptance Criteria

• The build identifies and documents the exact source/build stage that introduces core-js compatibility code.
• The published experiments artifact no longer contains bundled core-js global patches that modern supported consumers do not need.
• Jitsu/analytics transport code is externalized, modernized, or loaded only when experiments require it.
• sideEffects metadata is added only after verifying that shipped modules are side-effect safe.
• A real consumer fixture records raw, minified, and gzip sizes before and after the change.
• A bundle-size budget prevents reintroducing the current approximately 41.5 KB gzip cost.
• Experiment assignment, persistence, redirects, click tracking, and analytics events continue to work.
• Supported browser targets are documented and tested.

Priority

High

Additional Context

Do not solve this issue by setting sideEffects: false on the current artifact. That flag is a behavioral promise; it would be unsafe while module evaluation contains global-patching code.

Start with core-web/libs/sdk/experiments/rollup.config.cjs and the source entry points in src/index.ts, src/lib/components/withExperiments.tsx, and src/lib/dot-experiments.ts. Compare them with core-web/dist/libs/sdk/experiments/index.esm.js to trace the stage introducing core-js, then measure a real consumer fixture before and after. Done means the artifact avoids unwanted bundled global patches, required experiment behavior remains intact, and supported browsers and a size budget are documented and tested.