fix: rewrite SSR client-side hydration

[johnjenkins]

What is the current behavior?

There are lots of rough edges around the use of Stencil's proprietary non-shadow components during SSR

GitHub Issue Number:

• Fixes bug: incorrect 'slot forwarding' when mixing shadow: true and scoped: true components during SSR hydration  #6065
• Fixes bug: slotted scoped: true component gets duplicated during SSR hydration #6064
• Fixes bug: slotting content in a scoped: true component changes order of markup during SSR hydration #6063
• Fixes bug: scoped: true component slot fallback content gets hidden during SSR hydration #6062
• Fixes bug: Hydrate SSR Issue – Incorrect order of children elements after renderToString()  #5198

What is the new behavior?

A partial re-write of client-hydrate.ts (and few minor tweaks in the accompanying files) fixes all these issues.

Documentation

Does this introduce a breaking change?

• Yes
• No

^ no breaking changes, but I should mention that during / after hydrating now, there are some changes to the outputted markup:

• A couple more internal tags / comments from the server generated markup
• Fewer Stencil-generated comment nodes left behind after hydration

These changes could potentially cause users' test snapshots to fail.

Users would just need to update their snapshots

Testing

New spec tests. New e2e tests.

Other information

Referring to the linked issues, here's the same repo with the fixes applied:

I appreciate, with a re-factor to client-hydrate.ts this big, there's a degree of 'trust me bra' involved - it's difficult to grok. I've done my best to add lots of comments to help elucidate it's dark magic, but if it's too much or too little just let me know. If you'd like me to talk through what it's doing just let me know :)