GPv3: Normalize Stroke operator

This operator has the same functionality that GPv2 version.

Note: The radius is set with the entry value. In GPv2 the radius
was relative to the stroke thickness. Maybe we need review this.

@@ -951,0 +970,4 @@
+    {int(NormalizeMode::OPACITY),
+     "OPACITY",
+     0,
+     "OPacity",

@@ -951,0 +1033,4 @@
+            }
+            else if (mode == NormalizeMode::OPACITY) {
+              opacities[point_i] = opacity;
+              CLAMP(opacities[point_i], 0.0f, 1.0f);

@@ -951,0 +1019,4 @@
+        }
+
+        const OffsetIndices<int> points_by_curve = curves.points_by_curve();
+        selected_curves.foreach_index([&](const int curve_index) {

@@ -951,0 +1026,4 @@
+        if (mode == NormalizeMode::THICKNESS) {
+          bke::curves::fill_points<float>(points_by_curve, selected_curves, radius, radii);
+        }
+        if (mode == NormalizeMode::OPACITY) {

@@ -951,0 +961,4 @@
+  OPACITY,
+};
+
+static const EnumPropertyItem prop_normalize_modes[] = {

@@ -951,0 +1020,4 @@
+        }
+
+        const OffsetIndices<int> points_by_curve = curves.points_by_curve();
+        MutableSpan<float> radii = drawing.radii_for_write();

@@ -960,0 +1014,4 @@
+  ot->flag = OPTYPE_REGISTER | OPTYPE_UNDO;
+
+  /* props */
+  ot->prop = RNA_def_float(

@@ -26,6 +27,9 @@
 #include "ED_grease_pencil.hh"
 #include "ED_screen.hh"
 
+#include "UI_interface.hh"