Add @sentry/types and rrweb-snapshot as dev dependencies

This is neccessary to resolve re-exported types referred to by posthog-js' type definitions.

This isn't ideal, but

* We intend to start using sentry anyway
* Discussion with posthog maintainers about rrweb-snapshot at https://github.com/PostHog/posthog-js/issues/252, perhaps we can find another solution soon

package.json

@@ -124,6 +124,7 @@
     "@babel/traverse": "^7.12.12",
     "@matrix-org/olm": "https://gitlab.matrix.org/api/v4/projects/27/packages/npm/@matrix-org/olm/-/@matrix-org/olm-3.2.3.tgz",
     "@peculiar/webcrypto": "^1.1.4",
+    "@sentry/types": "^6.10.0",
     "@sinonjs/fake-timers": "^7.0.2",
     "@types/classnames": "^2.2.11",
     "@types/commonmark": "^0.27.4",
@@ -167,6 +168,7 @@
     "matrix-web-i18n": "github:matrix-org/matrix-web-i18n",
     "react-test-renderer": "^17.0.2",
     "rimraf": "^3.0.2",
+    "rrweb-snapshot": "1.1.7",
     "stylelint": "^13.9.0",
     "stylelint-config-standard": "^20.0.0",
     "stylelint-scss": "^3.18.0",