UI: Theme: Update Curves Handle Type colors

This PR Updates the default colors of the Curve Handle types,
to increase readability and contrast.
Each color more different from each other to not be confusing.

Logic for the new colors:
* Purple/Dark blue is used for the `Vector` type to match the header
  and sockets of Vector nodes.
* Red is used for `Auto` to show that they're locked and can't be
  changed without converting the type.
* Pink/Salmon color is used for `Auto-Clamped`  to be similar to `Auto`
   while still being distinct.
* The remaining colors are chosen to be visually distinct from the
  other colors.

This also fixes a problem caused by 1067112c11 (#145360) where
Free handle were left fully black. These black handles are extremely
hard to use with Grease Pencil objects, because Grease Pencil strokes
often are black. Because the `Free` handle selected color is also black,
handles do not show if they are selected.

Co-authored-by: Nika Kutsniashvili <nickberckley@gmail.com>
Pull Request: https://projects.blender.org/blender/blender/pulls/147335

release/datafiles/userdef/userdef_default_theme.c

@@ -334,16 +334,16 @@ const bTheme U_theme_default = {
       .long_key_selected = RGBA(0xff8c0099),
     },
     .curves = {
-      .handle_free = RGBA(0x000000ff),
-      .handle_auto = RGBA(0x909000ff),
-      .handle_vect = RGBA(0x409030ff),
-      .handle_align = RGBA(0x803060ff),
-      .handle_auto_clamped = RGBA(0x994030ff),
-      .handle_sel_free = RGBA(0x000000ff),
-      .handle_sel_auto = RGBA(0xf0ff40ff),
-      .handle_sel_vect = RGBA(0x40c030ff),
-      .handle_sel_align = RGBA(0xf090a0ff),
-      .handle_sel_auto_clamped = RGBA(0xf0af90ff),
+      .handle_free = RGBA(0x745900ff),
+      .handle_auto = RGBA(0x740d00ff),
+      .handle_vect = RGBA(0x232374ff),
+      .handle_align = RGBA(0x157000ff),
+      .handle_auto_clamped = RGBA(0x803060ff),
+      .handle_sel_free = RGBA(0xffc300ff),
+      .handle_sel_auto = RGBA(0xff1900ff),
+      .handle_sel_vect = RGBA(0x4444ffff),
+      .handle_sel_align = RGBA(0x72ff57ff),
+      .handle_sel_auto_clamped = RGBA(0xf090a0ff),
       .handle_vertex = RGBA(0x000000ff),
       .handle_vertex_select = RGBA(0xff8500ff),
       .handle_vertex_size = 5,

scripts/presets/interface_theme/Blender_Light.xml

@@ -449,16 +449,16 @@
         </anim>
         <curves>
           <ThemeCommonCurves
-            handle_free="#000000"
-            handle_sel_free="#000000"
-            handle_auto="#909000"
-            handle_sel_auto="#f0ff40"
-            handle_vect="#409030"
-            handle_sel_vect="#40c030"
-            handle_align="#803060"
-            handle_sel_align="#f090a0"
-            handle_auto_clamped="#994030"
-            handle_sel_auto_clamped="#f0af90"
+            handle_free="#745900"
+            handle_sel_free="#ffc300"
+            handle_auto="#740d00"
+            handle_sel_auto="#ff1900"
+            handle_vect="#232374"
+            handle_sel_vect="#4444ff"
+            handle_align="#157000"
+            handle_sel_align="#72ff57"
+            handle_auto_clamped="#803060"
+            handle_sel_auto_clamped="#f090a0"
             handle_vertex="#000000"
             handle_vertex_select="#ff8500"
             handle_vertex_size="5"