search: Rename search stack code to notepad

Created by: fkling

This PR renames all occurrences and variances of "search stack" to notepad, deprecates the feature flag and fixes tests and stories that where still using the experimental feature flag.

Test plan

For inspecting storybook:

yarn storybook

For verifying tests:

yarn test -- --testPathPattern=notepad

For making sure that TS is happy:

yarn build-ts