ArgGroup synopsis should respect order (if specified)

[remkop]

See this StackOverflow question: https://stackoverflow.com/questions/60424395/cannot-create-cli-with-specific-with-synopsis-cli-with-picocli

It turns out that the order of elements in the synopsis cannot be affected by the order attribute.
Investigate if it is feasible to control the synopsis with the order attribute.

---

Note to self:

Index: src/main/java/picocli/CommandLine.java
IDEA additional info:
Subsystem: com.intellij.openapi.diff.impl.patch.CharsetEP
<+>UTF-8
===================================================================
--- src/main/java/picocli/CommandLine.java	(date 1582775601204)
+++ src/main/java/picocli/CommandLine.java	(date 1582775601204)
@@ -8893,18 +8893,28 @@
             private Text rawSynopsisUnitText(Help.ColorScheme colorScheme, Set<ArgSpec> outparam_groupArgs) {
                 String infix = exclusive() ? " | " : " ";
                 Text synopsis = colorScheme.ansi().new Text(0);
+
+                List<IOrdered> sortableComponents = new ArrayList<IOrdered>();
+                List<PositionalParamSpec> remainder = new ArrayList<PositionalParamSpec>();
                 for (ArgSpec arg : args()) {
+                    if (arg instanceof OptionSpec) { sortableComponents.add((IOrdered) arg); }
+                    else { remainder.add((PositionalParamSpec) arg); }
+                }
+                sortableComponents.addAll(subgroups());
+                Collections.sort(sortableComponents, new Help.SortByOrder<IOrdered>());
+                for (IOrdered ordered : sortableComponents) {
                     if (synopsis.length > 0) { synopsis = synopsis.concat(infix); }
-                    if (arg instanceof OptionSpec) {
-                        synopsis = concatOptionText(synopsis, colorScheme, (OptionSpec) arg);
+                    if (ordered instanceof OptionSpec) {
+                        synopsis = concatOptionText(synopsis, colorScheme, (OptionSpec) ordered);
+                        outparam_groupArgs.add((OptionSpec) ordered);
                     } else {
-                        synopsis = concatPositionalText(synopsis, colorScheme, (PositionalParamSpec) arg);
+                        synopsis = synopsis.concat(((ArgGroupSpec) ordered).synopsisText(colorScheme, outparam_groupArgs));
                     }
-                    outparam_groupArgs.add(arg);
                 }
-                for (ArgGroupSpec subgroup : subgroups()) {
+                for (PositionalParamSpec positional : remainder) {
                     if (synopsis.length > 0) { synopsis = synopsis.concat(infix); }
-                    synopsis = synopsis.concat(subgroup.synopsisText(colorScheme, outparam_groupArgs));
+                    synopsis = concatPositionalText(synopsis, colorScheme, (PositionalParamSpec) positional);
+                    outparam_groupArgs.add(positional);
                 }
                 return synopsis;
             }