Fix connected tab close button spacing

[Copilot]

Fixes the connected document tab close action spacing so terminal shoulders and wrapped pill insets reserve the same space around the action as ordinary connected tabs. This keeps the visible tab cap width stable when closing down to a single tab.

Adds a geometry regression test covering multiple, single, bottom-wrapped, and upper-wrapped states, plus a single-tab component fixture.

Validation:

• npm run eslint -- src/vs/workbench/test/browser/parts/editor/multiEditorTabsControl.test.ts src/vs/workbench/test/browser/componentFixtures/editor/editorTabBar.fixture.ts
• npm run stylelint -- src/vs/workbench/contrib/modernUI/browser/media/connectedEditorTabs.css
• Core compile emitted the affected sources with zero TypeScript errors; the secondary typecheck process was killed by the constrained environment.
• Targeted browser geometry test could not run locally because Playwright system dependencies are unavailable behind the environment firewall.

[Copilot]

🟡 Changes recommended

Left-positioned tab actions still allow the terminal shoulder inset to shrink the visible tab cap.

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Pull request overview

Adjusts connected-tab close-button spacing to keep tab geometry consistent across terminal and wrapped states.

Changes:

• Updates connected-tab action padding and positioning.
• Adds geometry regression coverage.
• Adds a single-tab visual fixture.

File summaries

File	Description
connectedEditorTabs.css	Adjusts close-action spacing.
multiEditorTabsControl.test.ts	Tests connected-tab geometry states.
editorTabBar.fixture.ts	Adds a single-tab fixture.

Review details

• Files reviewed: 3/3 changed files
• Comments generated: 1
• Review effort level: Balanced

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[Copilot]

Added explicit close-action hover fixtures for the critical terminal layouts: single tab, last tab in a multi-tab row, upper wrapped row, and bottom wrapped row. These show the actual hover background so its inset spacing can be visually compared. Also narrowed width reservation to stable logical terminals, avoiding the viewport-edge geometry feedback loop seen in browser/Electron CI.