chore: remove deprecated contextmenu html global attribute

[ekashida]

Details

Remove support for contextmenu global html attribute that was only ever implemented in Firefox and has since been removed from Firefox.

Does this pull request introduce a breaking change?

Unlikely, as there isn't a single browser that does anything with this attribute. Even when it was implemented, it was only supported by Firefox.

[nolanlawson]

Does this have the potential for breaking changes? Why remove it?

[ekashida]

@nolanlawson I'm proposing to remove it because it didn't feel right adding reflection support for it in ssr-compiler and engine-server.

[ekashida]

I was doing the breaking change analysis that we discussed earlier when I realized that CSR doesn't even provide reflection for contextmenu. These global attributes are the only ones that reflect in LWC, so engine-dom does not apply any special treatment for contextmenu aside from the "ambiguous property" compiler error.

Current engine-server behavior for contextmenu:

• ❌ When set as property, reflects as an attribute
• When set as an attribute (declarative)
  • ✅ Host element renders the attribute
  • ✅ Does not reflect as a property
• ✅ When set as an attribute (imperative)
  • ✅ Does not reflect as a property

So the only thing that this PR will break is that setting this.contextMenu will no longer reflect as an attribute in engine-server.

[nolanlawson]

Mildly breaking for engine-server, so low-risk. Let's do it!