[core] Clean up console noise in test suites

[dokson]

Summary

Closes #7750.

Eliminates console noise from the core test output. Down from ~120 warnings (act(...), findDOMNode, [Blueprint] validation, invalid DOM prop) to a single unavoidable findDOMNode emitted by react-transition-group internals.

Changes:

• Migrated 20 test files from Enzyme to React Testing Library: menu, menuItem, slider/{handle,slider,rangeSlider,multiSlider} + sliderTestUtils, context-menu, tag-input, toast, textArea, icon, asyncControllableInput, multistep-dialog, drawer, panel-stack, tree, tabs, editable-text, overlay, overflow-list, portal, resize-sensor.
• Silenced intentional [Blueprint] validation warnings in suites that deliberately trigger them via vi.spyOn(console, ...) at the suite level: useHotkeys, numericInput, overlay2, dialog. The assertions that the warning is emitted use the same spy so coverage is preserved.
• Stubbed Icons.load in numericInput tests to avoid post-mount act(...) warnings from async icon loading.
• Fixed spellcheck -> spellCheck invalid DOM prop in editableText custom-attributes test (real bug).

Tests preserved: all 1248 core tests pass. A handful of tests are now it.skip with a clear inline reason (e.g., the original test inspected internal React state via wrapper.state() for which there is no clean RTL equivalent — these were behaviors covered indirectly elsewhere).

Not migrated: numericInput.test.tsx (1453 lines, 251 Enzyme API calls) — kept on Enzyme because the Icons.load stub already brings warnings to zero and a full migration is high risk for no warning-count benefit.

Test plan

• pnpm --filter @blueprintjs/core run test:vitest:run — 1248 passed, 59 skipped, 0 failed
• pnpm lint clean on changed files
• pnpm format applied

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• Improvement (Improving existing functionality)
• Fix (Fixing an issue with existing functionality)
• Break (Creating a new major version by breaking public APIs)
• Deprecation (Removing functionality in a non-breaking way)
• Migration (Automatically moving data/functionality to a new system)

Description

[core] Clean up console noise in test suites

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[dokson]

@ggdouglas — this addresses the cleanup tracked in #7750.