[context] Use stopImmediatePropagation()

Proposal: Common public interface for ElementInternals

[performance-markers] initial proposal (WIP)

[slottable-request] Use Symbol.for() for the remove sentinel value

Updates template status to "Proposal" as that is the first stage of a community protocol.

[On-Demand Definitions] Initial draft

Adding simple slottable request example

[context] recommend to keep weak references to subscribers

fix: minor copyedits on README.md

Add a proposal template