Perf: Introduce clearPreviousFieldValues for mitigation of React fiber memory issue

[leeoniya]

this is a beautiful gross hack to mitigate a memory issue with React's concurrent [Fiber] reconciler, which was rolled out with React 16....in late 2017 😅

while we await a final decision on facebook/react#36176, we can mostly side-step the badness of having 2x the query response data in memory at all times (previous and current). for dashboards with many and/or heavy queries this results in potentially 100MB+ of RAM savings per browser tab/dashboard.

i think this changeset is the minimal one, placed right at the entry point where panel data gets passed down through react props/state to the panel plugin components.

is this mutation risky?

in my opinion the risk is very low. relying on the previous field value arrays to stay filled with old data is nothing i have ever seen in practice. a smoke test in grafana core shows no related test failures: grafana/grafana#120190

nevertheless, this will be feature-gated behind clearPreviousFieldValues .

once this code is running in ops i will toggle it via localstorage to smoke test some real dashboards before rolling anything out. if that feels bug-free, we can start to roll it to dev/staging/free/canary/paid etc.

best case: meta fixes this misfeature in fiber
next best case: it becomes default enabled for all grafana users
worst case: it stays experimental or private preview and heavy users can opt into it

testing with single debug panel, random walk, 1,000 series * 1,440 points, multiple data refreshes:

before:

---

after:

---

📦 Published PR as canary version: 7.3.6--canary.1392.23904848795.0

✨ Test out this PR locally via:

npm install @grafana/scenes@7.3.6--canary.1392.23904848795.0
npm install @grafana/scenes-react@7.3.6--canary.1392.23904848795.0
# or 
yarn add @grafana/scenes@7.3.6--canary.1392.23904848795.0
yarn add @grafana/scenes-react@7.3.6--canary.1392.23904848795.0

[clord]

readonly arrays or object.frozen arrays might throw a TypeError. but other than that this is a decent hack.

[leeoniya]

never seen frozen stuff come out of DS. possible in theory, but i'll put money on it never happening in practice.

[dprokop]

LGTM, but please let's get rid of feature toggles reference in scenes.

[scenes-repo-bot-access-token]

🚀 PR was released in v7.3.6 🚀