Remove dependency on FormToolkit, ExpandableComposite, and ScrolledForm
in ChooseWorkspaceDialog and ChooseWorkspaceWithSettingsDialog. Replace
with plain SWT composites and Labels with Unicode triangle characters
(U+25B8 ▸ / U+25BE ▾) for the expand/collapse toggle.

This improves dialog startup performance by eliminating the Forms
overhead: extra decorated composites, global paint/focus listeners,
color management, and recursive ScrolledForm reflow on each toggle.

The Unicode triangles are from the Geometric Shapes block (Unicode 1.0)
and render reliably on Windows, macOS, and Linux system fonts.

Also fix layout data mismatch where the path Combo used GridData inside
a BorderLayout container (now uses BorderData).