[delegatesFocus] Shadow host should receive focus event when focus enters the shadow tree

[ekashida]

Description

The host element should always receive the focus event whenever focus enters the shadow tree, regardless of the delegatesFocus or tabindex value (needs spec verification).

The current workaround is for the component to dispatch a focus event when it detects focus inside the shadow tree.

Steps to Reproduce

1242

[ekashida]

Possible solution: Dispatch focus when needed, but need to investigate concerns around isTrusted and whether relatedTarget gets set correctly.

[ekashida]

Also, don't forget about blur.

[gonzalocordero]

@ekashida @gregwhitworth now that we are doing native shadow, this might be a good time to revisit this issue.

[nolanlawson]

Another difference in native shadow and synthetic shadow was discovered around this.

Standard focus and blur events work differently. Consider a focusable element like:

<template>
   <input type="text">
</template>

In synthetic shadow, focus and blur do not bubble up. E.g.:

<lightning-component 
  onfocus={iWillNotBeExecuted} 
  onblur={iWillNotBeExecuted}
></lightning-component>

In native shadow, blur and focus do bubble:

<lightning-component 
  onfocus={iWillBeExecutedIfInputisFocussed} 
  onblur={iWillBeExecutedIfInputIsBlurred}
></lightning-component>

(/ht to John Hefferman for this.)