Browser support (take 2)

[kraenhansen]

What, How & Why?

The work in #5895 has rotted a bit and we want to ensure this gets merged.
One blocker of that was the need for a top-level await of the WASM native module, which we cannot export as our module is currently CommonJS (uses require statements, which doesn't support top-level await semantics).

As outlined in the original proposal for the top-level await language feature:

In the absence of this feature, it's possible to export a Promise from a module, and wait on that to know when its exports are ready.

And until our SDK exports as ESM, I suggest we export a ready promise which must be awaited until interacting with the SDK on platforms which load the native module asynchronously.

NOTE: This PR currently targets kh/wrapper-refactored (which in turn targets kh/avoid-circular-imports) and need to be re-based once it's merged.
NOTE: This also needs to #6820

☑️ ToDos

• Update to use the unified "wrapper.ts" instead of implementing a "wasm-wrapper.ts" template which depends on the (now deleted) base-wrapper.ts
• 📝 Changelog entry
• 📝 Compatibility label is updated or copied from previous entry
• 📝 Update COMPATIBILITY.md
• 🚦 Tests
• 📦 Updated internal package version in consuming package.jsons (if updating internal packages)
• 📱 Check the React Native/other sample apps work if necessary
• 💥 Breaking label has been applied or is not necessary
• 🔔 Mention @realm/devdocs if documentation changes are needed