Add widget screenshot requirements and update some out of date fields

[amandabaker]

Rendered article for review:
https://review.learn.microsoft.com/microsoft-edge/progressive-web-apps-chromium/how-to/widgets?branch=pr-en-us-2858
[Before]

Changes made by this PR:

• Noted the limitation of both widget screenshots and icons to a max of 1024x1024 pixels.
• Updated the matchAll options from instance and host to instanceId and hostId.
• Added multiple to the widget definition.
• Updated the type of widget on the WidgetEvent from WidgetInstance to Widget.
• Added a note that a WidgetClickEvent allows the SW to open a window in response to the event.

AB#46944432

[amandabaker]

@captainbrosset Would you PTAL? I'm not sure about the wording of the WidgetClick event bit at the end, so lmk if you have suggestions on how to better word that.

[learn-build-service-prod]

Learn Build status updates of commit 9f55a54:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/progressive-web-apps-chromium/how-to/widgets.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel

[mikehoffms]

Writer/Editor pass, from the Files Changed POV.

[captainbrosset]

Minor suggestion for the widgetclick event. PR looks great otherwise. Thank you Amanda.

[learn-build-service-prod]

Learn Build status updates of commit bde980b:

✅ Validation status: passed

File	Status	Preview URL	Details
microsoft-edge/progressive-web-apps-chromium/how-to/widgets.md	✅Succeeded	View

For more details, please refer to the build report.

For any questions, please:

• Try searching the learn.microsoft.com contributor guides
• Post your question in the Learn support channel