[dagit] Lazy import CodeMirror
Remove CodeMirror from the main vendor bundle by using React.lazy on ExecutionSessionContainer, the only use case of the CodeMirror package in Dagit. ExecutionSessionContainer also becomes its own chunk, which reduces the application bundle as well.
File sizes after gzip: Before: 669.66 KB build/static/js/2.d336297b.chunk.js 153.37 KB build/static/js/main.9dc0e9c2.chunk.js 33.92 KB build/static/css/2.56579013.chunk.css 32.28 KB build/922792c33f2e681c1472.worker.js 771 B build/static/js/runtime-main.8b1ec68b.js 326 B build/static/css/main.af0c7fcc.chunk.css After: 596.68 KB (-72.98 KB) build/static/js/2.98ac1f77.chunk.js 143.01 KB (-10.36 KB) build/static/js/main.0f2746db.chunk.js 72.93 KB build/static/js/3.a76ca228.chunk.js 32.28 KB build/922792c33f2e681c1472.worker.js 31.38 KB (-2.54 KB) build/static/css/2.bc62a557.chunk.css 14.61 KB build/static/js/4.cacb1563.chunk.js 2.93 KB build/static/css/3.4439d99d.chunk.css 1.48 KB (+747 B) build/static/js/runtime-main.efbdbfc2.js 326 B build/static/css/main.af0c7fcc.chunk.css
This isn't anything earth-shattering right now, but as we add more features and complexity, it would be good to have good hygiene and make use some of these cool lazy-loading features to keep bundle size manageable.
Test Plan: Buildkite, sanity check Dagit by navigating to pipeline playground. Verify that everything loads as expected, and that the new bundles are loaded lazily.
Reviewers: bengotow, prha, sashank
Reviewed By: prha
Differential Revision: https://dagster.phacility.com/D6072