buttons cut off last selection drop down when using CustomUI

[ajshedivy]

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Describe the bug When working with tabs with CustomUI, I'm noticing that when I add a group of buttons to a ui (after adding tabs), that the last drop down selection box is cut off. Here is code to reproduce:

To Reproduce Steps to reproduce the behavior:

  const base = loadBase();
  const ui = base.customUI();
  const myTab = base.customUI();
  myTab
    .addSelect(`auto commit`, `Auto commit`, [
      {value: `true`, description: `True`, text: `Commit (true)`, selected: options["auto commit"] === `true`},
      {value: `false`, description: `False`, text: `No commit (false)`, selected: options["auto commit"] === `false`}]);

  let tabs: ComplexTab[] = [
    {label: `My Properties`, fields: myTab.fields}
  ];

  ui.addComplexTabs(tabs)
    .addButtons(
      {id: `apply`, label: `Apply changes`},
      {id: `cancel`, label: `Cancel`},
  );

Expected behavior The drop down options are not cut off by buttons:

The current workaround is to add the buttons to the end of each tab, but when working with multiple tabs this adds repeated code:

  const base = loadBase();
  const ui = base.customUI();
  const myTab = base.customUI();
  myTab
    .addSelect(`auto commit`, `Auto commit`, [
      {value: `true`, description: `True`, text: `Commit (true)`, selected: options["auto commit"] === `true`},
      {value: `false`, description: `False`, text: `No commit (false)`, selected: options["auto commit"] === `false`}])
      .addButtons(
        {id: `apply`, label: `Apply changes`},
        {id: `cancel`, label: `Cancel`},
    );

  let tabs: ComplexTab[] = [
    {label: `My Properties`, fields: myTab.fields}
  ];

  ui.addComplexTabs(tabs)

Screenshots If applicable, add screenshots to help explain your problem.

Environment (please complete the following information):

• Extension version v1.9.4
• IBM i OS version 7.4

Additional context vscode-db2i extension: https://github.com/halcyon-tech/vscode-db2i/pull/9