Fix clipped dropdowns in connection form

[DaveT1991]

Fixes #65007

Connection form dropdowns can be clipped inside the dialog and accordion layout, which makes some values inaccessible when a custom connection field exposes a long enum list.

This change renders the affected chakra-react-select menus in a portal attached to document.body, uses menuPosition="fixed", and applies a modal-safe z-index so the dropdown list can escape the accordion/container clipping and remain fully visible.

Changes:

• add shared portalled select menu styling for connection-form selects
• apply the shared portal configuration to flexible-form single-select fields
• apply the shared portal configuration to flexible-form multi-select fields
• apply the same portal configuration to the connection type and team selectors
• add a regression test asserting the flexible-form dropdown uses the portalled menu configuration

Validation:

• pnpm exec eslint src/utils/advancedSelectStyles.ts src/components/FlexibleForm/FieldDropdown.tsx src/components/FlexibleForm/FieldMultiSelect.tsx src/components/TeamSelector.tsx src/pages/Connections/ConnectionForm.tsx src/components/FlexibleForm/FieldDropdown.test.tsx
• pnpm exec vitest run src/components/FlexibleForm/FieldDropdown.test.tsx

[bbovenzi]

Cool! Can you provide a screenshot of before and after?

[DaveT1991]

Cool! Can you provide a screenshot of before and after?

Before:

After:

[Copilot]

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[kaxil]

Cool! Can you provide a screenshot of before and after?

Before:

After:

This isn't the screenshot of Airflow UI!