Missing contextMenuBuilder support in CodeField

[yogitah-mecha]

Problem

CodeField does not expose a way to customize the text selection context menu
(copy / select all / custom actions), unlike Flutter's TextField and
EditableText, which provide contextMenuBuilder.

This makes it impossible to:

• Customize the selection toolbar
• Add app-specific actions (Search, Format, Go to line, etc.)
• Match platform behavior or design requirements

---

What works in TextField

TextField(
  contextMenuBuilder: (context, editableTextState) {
    return AdaptiveTextSelectionToolbar(
      anchors: editableTextState.contextMenuAnchors,
      children: const [
        SelectionOptions(),
      ],
    );
  },
)

---

Current CodeField API

CodeField(
  controller: _codeController,
  textStyle: const TextStyle(fontFamily: 'monospace'),
)

There is currently no way to pass a contextMenuBuilder or otherwise customize
the selection toolbar.

Request / Proposal

Expose a contextMenuBuilder (or equivalent) on CodeField, and forward it
internally to the underlying EditableText.

Example API:

CodeField(
  controller: _codeController,
  contextMenuBuilder: (context, editableTextState) {
    return AdaptiveTextSelectionToolbar(
      anchors: editableTextState.contextMenuAnchors,
      children: const [
        SelectionOptions(),
      ],
    );
  },
)