Batch ListView horizontal width measurement

[ulugbekna]

Summary

• batch horizontal row width measurement into write, read, and reset phases
• apply batching to visible-row insertion, range scrolling, and runtime horizontal-scrolling enablement
• preserve per-row padding calculations, width caching, and deferred scroll-width updates

The dynamic-height probe remains separate; ListView rejects combining dynamic heights with horizontal scrolling.

Verification

• added a deterministic ListView test proving all five fit-content writes precede all five offsetWidth reads for splice, scroll/reuse, and enablement paths
• verified per-row padding arithmetic and row-width resets
• npm run typecheck-client
• targeted ListView unit suite
• npm run valid-layers-check
• staged pre-commit hygiene

Fixes #326639

cc @roblourens

[vs-code-engineering]

📬 CODENOTIFY

The following users are being notified based on files changed in this PR:

@benibenj

Matched files:

• src/vs/base/browser/ui/list/listView.ts

[Copilot]

Pull request overview

Batches ListView horizontal row-width measurements to reduce repeated browser layouts.

Changes:

• Separates width writes, reads, and resets into batch phases.
• Applies batching to insertion, scrolling, and runtime enablement paths.
• Adds deterministic coverage for ordering, padding, caching, and resets.

Show a summary per file

File	Description
src/vs/base/browser/ui/list/listView.ts	Implements batched row-width measurement.
src/vs/base/test/browser/ui/list/listView.test.ts	Verifies batching and width calculations.

Review details

• Files reviewed: 2/2 changed files
• Comments generated: 0
• Review effort level: Medium

[roblourens]

Not sure why the cc for me, am I supposed to know anything about this? 😅

[ulugbekna]

@roblourens agent somehow thought you were the owner, but yeah, it's for Ben

[ulugbekna]

@benibenj I'm going ahead with merging to get more selfhosting time. We can revert if you don't like the change when you're back