Draft: ShapeString: use an actual font file as default, allow TTC files

* To help novice users supply an actual font file from the OS as the default for ShapeStringFontFile.
* The Draft code blocked the use of TTC font files. `Part.makeWireString()` can however handle them (although only the first font in the file can be used).

Additonally:
In a previous PR the bottom spacer was removed from the task panel. This PR brings it back as it is required in some cases. Without it  the "..." button of the file selector can become huge.

src/Mod/Draft/Resources/ui/TaskShapeString.ui

@@ -149,7 +149,7 @@ Uncheck to use working plane coordinate system</string>
           </property>
          </widget>
         </item>
-       <item row="0" column="1">
+        <item row="0" column="1">
          <widget class="QLineEdit" name="leText">
           <property name="toolTip">
            <string>Text to be made into ShapeString</string>
@@ -166,12 +166,19 @@ Uncheck to use working plane coordinate system</string>
         <item row="1" column="1">
          <widget class="Gui::FileChooser" name="fcFontFile">
           <property name="filter">
-           <string>Font files (*.ttf *.otf *.pfb *.TTF *.OTF *.PFB)</string>
+           <string>Font files (*.ttc *.ttf *.otf *.pfb *.TTC *.TTF *.OTF *.PFB)</string>
           </property>
          </widget>
         </item>
        </layout>
       </item>
+      <item row="2" column="0">
+       <spacer name="verticalSpacer_1">
+        <property name="orientation">
+         <enum>Qt::Vertical</enum>
+        </property>
+       </spacer>
+      </item>
      </layout>
     </widget>
    </item>

src/Mod/Draft/draftobjects/shapestring.py

@@ -146,7 +146,7 @@ class ShapeString(DraftObject):
             if not os.path.isfile(font_file):
                 _err(obj.Label + ": " + translate("draft", "Specified font file is not a file"))
                 return
-            if not os.path.splitext(font_file)[1].upper() in (".TTF", ".OTF", ".PFB"):
+            if not os.path.splitext(font_file)[1].lower() in (".ttc", ".ttf", ".otf", ".pfb"):
                 _err(obj.Label + ": " + translate("draft", "Specified font type is not supported"))
                 return
 

src/Mod/Draft/draftutils/params.py

@@ -391,15 +391,44 @@ def _param_from_PrefFontBox(widget):
     return path, entry, value
 
 
+def _get_shape_string_font_file():
+    """Try to get the file name of a sans serif font (TTC or TTF) from the OS."""
+    # https://forum.freecad.org/viewtopic.php?t=96770
+    # Windows font: "arial"
+    # Mac fonts: "geneva" and "helvetica"
+    # Linux fonts: "dejavusans" and "freesans"
+    favorite_names = ("arial", "geneva", "helvetica", "dejavusans", "freesans")
+    font_file_sans = None   # Font with name containing "sans". 1st fallback.
+    font_file_alpha = None  # Font with name starting with a letter. 2nd fallback.
+    # Reverse the order of the paths so that user related paths come last:
+    for path in QtCore.QStandardPaths.standardLocations(QtCore.QStandardPaths.FontsLocation)[::-1]:
+        # We don't use os.path.join as dir_path has forward slashes even on Windows.
+        for (dir_path, dir_names, file_names) in os.walk(path):
+            for file_name in file_names:
+                base_name, ext = [s.lower() for s in os.path.splitext(file_name)]
+                if not ext in (".ttc", ".ttf"):
+                    continue
+                if base_name in favorite_names:
+                    return dir_path + "/" + file_name
+                if font_file_sans is None and "sans" in base_name:
+                    font_file_sans = dir_path + "/" + file_name
+                if font_file_alpha is None and base_name[0].isalpha():
+                    font_file_alpha = dir_path + "/" + file_name
+    if font_file_sans is not None:
+        return font_file_sans
+    if font_file_alpha is not None:
+        return font_file_alpha
+    return ""
+
+
 def _get_param_dictionary():
 
     # print("Creating preferences dictionary...")
 
     param_dict = {}
 
-    hatch_pattern_file = os.path.join(
-        App.getResourceDir().replace("\\", "/"), "Mod/TechDraw/PAT/FCPAT.pat"
-    )
+    hatch_pattern_file = App.getResourceDir().replace("\\", "/").rstrip("/") \
+            + "/Mod/TechDraw/PAT/FCPAT.pat"
 
     # Draft parameters that are not in the preferences:
     param_dict["Mod/Draft"] = {
@@ -437,7 +466,7 @@ def _get_param_dictionary():
         "ScaleCopy":                   ("bool",      False),
         "ScaleRelative":               ("bool",      False),
         "ScaleUniform":                ("bool",      False),
-        "ShapeStringFontFile":         ("string",    ""),
+        "ShapeStringFontFile":         ("string",    _get_shape_string_font_file()),
         "ShapeStringHeight":           ("float",     10.0),
         "ShapeStringText":             ("string",    translate("draft", "Default")),
         "snapModes":                   ("string",    "100000000000000"),