Feat: Add support for replaying :defined pseudo-class of custom elements (#1155)

* Feat: Add support for replaying :defined pseudo-class of custom elements

* add isCustom flag to serialized elements

Applying Justin's review suggestion

* fix code lint error

* add custom element event

* fix: tests (#1348)

* Update packages/rrweb/src/record/observer.ts

* Update packages/rrweb/src/record/observer.ts

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Co-authored-by: Nafees Nehar <nafees87n@gmail.com>
Co-authored-by: Justin Halsall <Juice10@users.noreply.github.com>

packages/rrweb-snapshot/test/__snapshots__/integration.test.ts.snap

@@ -839,6 +839,7 @@ exports[`shadow DOM integration tests snapshot shadow DOM 1`] = `
                   \\"isShadow\\": true
                 }
               ],
+              \\"isCustom\\": true,
               \\"id\\": 16,
               \\"isShadowHost\\": true
             },