cdp: Implement DOM.describeNode

[krichprollsch]

We want to implement DOM.describeNode which is required for puppeteer click scenario.

How to reproduce?

Use puppeteer/click.js scenario from the demo repository.

• start the demo webserver with $ go run ws/main.go
• optionnally use cdpproxy to log all cdp messages
• start Lightanda browser
• run the scenario node puppeteer/click.js

Current result

> {"method":"Runtime.callFunctionOn","params":{"functionDeclaration":"() => {\n                    return document;\n                }\n//# sourceURL=pptr:evaluateHandle;%23document%20(file%3A%2F%2F%2Fhome%2Fpierre%2Fwrk%2Fdemo%2Fnode_modules%2Fpuppeteer-core%2Flib%2Fesm%2Fpuppeteer%2Fapi%2FFrame.js%3A263%3A52)\n","executionContextId":2,"arguments":[],"returnByValue":false,"awaitPromise":true,"userGesture":true},"id":17,"sessionId":"SID-1"}
< {"id":17,"result":{"result":{"type":"object","subtype":"node","className":"HTMLDocument","description":"","objectId":"5987356902031041503.2.1"}},"sessionId":"SID-1"}
> {"method":"DOM.describeNode","params":{"objectId":"5987356902031041503.2.1"},"id":18,"sessionId":"SID-1"}
< {"id":18,"code":-31998,"message":"UnknownMethod"}