Design doc - Decoupling framework tests (#12626)

Added my design doc:
https://docs.google.com/document/d/1UHxALQqCbmgjnM1RNV9xE2pK3IGyx-UktGX1D7hYCjs/edit?pli=1&tab=t.0

Author: justinmc

firebase.json

@@ -357,6 +357,7 @@
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