feat(dimension): styled placement previews for creation commands

Show the styled dimension and its value while placing a dimension, using
the same builder the command commits with. Each creation command
(DIMLINEAR, DIMALIGNED, DIMANGULAR, DIMRADIUS, DIMDIAMETER, DIMARC,
DIMJOGGED, DIMORDINATE, DIMCONTINUE, DIMBASELINE, QDIM) reports the
dimensions it would commit at the current stage through
`CadCommand::dimension_preview`. The application applies the current
creation style, or the base dimension's style for DIMCONTINUEMODE=1,
and the same viewport measurement scale as commit, then tessellates the
transient entity through the normal dimension renderer.

While the second definition point is being acquired, a hovered model
snap supplies a provisional viewport scale; once both points are fixed,
hovering another viewport does not change the value. Angular dimensions
never receive length compensation. Degenerate geometry, an invalid
scale, or conflicting viewports fall back to the plain rubber-band
preview so no misleading value is shown.

src/modules/annotate/angular_dim.rs

@@ -7,8 +7,8 @@ use cadkernel::geom2d::{
 };
 
 use crate::command::{
-    CadCommand, CmdOption, CmdResult, DimensionAssociationInput,
-    DimensionAssociationSource, InputKind, WorkingPlane,
+    CadCommand, CmdOption, CmdResult, DimensionAssociationInput, DimensionAssociationSource,
+    DimensionPreview, InputKind, WorkingPlane,
 };
 use crate::modules::{IconKind, ModuleEvent, ToolDef};
 use crate::scene::model::wire_model::WireModel;
@@ -807,6 +807,32 @@ impl CadCommand for AngularDimensionCommand {
         };
         Some(preview_wire(points))
     }
+
+    fn dimension_preview(&self, cursor: DVec3) -> Option<Vec<DimensionPreview>> {
+        if self.selecting_object {
+            return None;
+        }
+        let result = match self.step {
+            Step::ArcPoint3 {
+                vertex,
+                first,
+                second,
+            } => self.finish_three_point(vertex, first, second, cursor),
+            Step::ArcPoint2 {
+                first_start,
+                first_end,
+                second_start,
+                second_end,
+            } => self.finish_two_line(first_start, first_end, second_start, second_end, cursor),
+            _ => return None,
+        };
+        match result {
+            CmdResult::CommitDimension { entity, .. } => {
+                Some(vec![DimensionPreview::current_style(entity)])
+            }
+            _ => Some(Vec::new()),
+        }
+    }
 }
 
 fn picked_curve(entity: &EntityType, click: DVec3) -> Option<PickedCurve> {