[combobox] Preserve inline input on Enter without highlight

[atomiks]

• I have followed (at least) the PR section of the contributing guide.

Pressing Enter with no highlighted item called setOpen(false), which triggered close/reset behavior and cleared inline input text. The fix skips that close call in inline mode, so Enter now leaves the typed value unchanged unless an item is actually highlighted and selected.

Fixes #4204

[pkg-pr-new]

• base-ui-tanstack-start

• vite-css-base-ui-example

  pnpm add https://pkg.pr.new/@base-ui/react@4235
  

  pnpm add https://pkg.pr.new/@base-ui/utils@4235
  

commit: e620820

[mui-bot]

Bundle size report

Bundle	Parsed size	Gzip size
@base-ui/react	🔺+12B(0.00%)	🔺+4B(0.00%)

Details of bundle changes

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