synthetic shadow polyfill

[caridy]

Tasks

• (in-progress) moving all shadow dom related polyfills into @lwc/synthetic-shadow new pkg
• refactor patch.ts to completely disconnect from polyfill. This includes:
  • enabling appendChild and co in ShadowRoot
  • change engine to use dot notation for the diffing algo instead of cached low level operations (this will represent a perf regression for sure turns out that it doesn't)
  • implement slotting manually in situ instead of the pre-allocation that we use today (that will make things slower as well... but will solve all the issues that we have with the connect/disconnect non-sense for slotted content.
  • refactor patching of node protos to be done in the polyfill instead of part of the diffing algo.
  • need a different mechanism to allow lwc:dom=manual, the current one is a hard connecting between engine and polyfill.
• change the distribution of the engine to NOT include the synthetic shadow out of the box, instead it should be included manually ahead of time.
  • change all apps (everybody)
  • change aura distro (@diervo)
  • change playground (@midzelis)
  • change jest tools (@trevor-bliss)
• consider removing the mutation observer in favor of a different mechanism to detect insertion and removal of non-registered custom elements across the board:
  • refactor upgrade.ts and wc.ts to rely on a different mechanism to detect insertion/removal
  • this will probably be another perf regression (review), but might help on the overall picture.
• some other cleanup
  • the presumption that compiler could provide specific hooks when detecting no-attribute, no-events, etc... seems wrong after some perf tests in the past, maybe we can remove that provision all together from engine/diffing