Fixes all TypeScript failures caused by enabling the `--strict`
flag for test source files. We also want to enable the strict
options for tests as the strictness enforcement improves the
overall codehealth, unveiled common issues and additionally it
allows us to enable `strict` in the `tsconfig.json` that is picked
up by IDE's.
PR Close#30993
This PR was merged without API docs and general rollout plan.
We can't release this as is in 5.1 without a plan for documentation, cli integration, etc.
Joey Perrott
Paul Gschwendtner
Andrew Seguin
Igor Minar
George Kalpakas