docs: add missing webview render-process-gone event

[miniak]

It should match the webContents events, which are used to implement the webview ones:

electron/docs/api/web-contents.md

Lines 463 to 496 in 9eeef55

	#### Event: 'crashed' _Deprecated_
	Returns:
	* `event` Event
	* `killed` boolean
	Emitted when the renderer process crashes or is killed.
	**Deprecated:** This event is superceded by the `render-process-gone` event
	which contains more information about why the render process disappeared. It
	isn't always because it crashed. The `killed` boolean can be replaced by
	checking `reason === 'killed'` when you switch to that event.
	#### Event: 'render-process-gone'
	Returns:
	* `event` Event
	* `details` Object
	* `reason` string - The reason the render process is gone. Possible values:
	* `clean-exit` - Process exited with an exit code of zero
	* `abnormal-exit` - Process exited with a non-zero exit code
	* `killed` - Process was sent a SIGTERM or otherwise killed externally
	* `crashed` - Process crashed
	* `oom` - Process ran out of memory
	* `launch-failed` - Process never successfully launched
	* `integrity-failure` - Windows code integrity checks failed
	* `exitCode` Integer - The exit code of the process, unless `reason` is
	`launch-failed`, in which case `exitCode` will be a platform-specific
	launch failure error code.
	Emitted when the renderer process unexpectedly disappears. This is normally
	because it was crashed or killed.

Except for the killed argument, which is not being forwarded:

electron/lib/browser/web-view-events.ts

Lines 24 to 25 in 9eeef55

	crashed: [],
	'render-process-gone': ['details'],

Also adds structures/render-process-gone-details.md to eliminate duplicates

Notes: none

[erickzhao]

docs: lgtm

[electron-docs-reviewer]

Approving on behalf of the Electron Docs Team

[miniak]

@zcbenz I think it can be merged now

[release-clerk]

No Release Notes

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