Adding "engine" chart for plantuml

Small chart example:
```
@startuml{chart}
h-axis "Quarters" [Q1, Q2, Q3, Q4] label-right
v-axis "Revenue ($K)" 0 --> 100
bar "Sales" [45, 62, 58, 70] #3498db
@enduml
```

Author: albert-github

addon/doxmlparser/doxmlparser/compound.py

@@ -1118,6 +1118,7 @@ class DoxPlantumlEngine(str, Enum):
     SALT='salt'
     MATH='math'
     LATEX='latex'
+    CHART='chart'
     GANTT='gantt'
     MINDMAP='mindmap'
     WBS='wbs'
@@ -24555,7 +24556,7 @@ def validate_DoxPlantumlEngine(self, value):
                 self.gds_collector_.add_message('Value "%(value)s"%(lineno)s is not of the correct base simple type (str)' % {"value": value, "lineno": lineno, })
                 return False
             value = value
-            enumerations = ['uml', 'bpm', 'wire', 'dot', 'ditaa', 'salt', 'math', 'latex', 'gantt', 'mindmap', 'wbs', 'yaml', 'creole', 'json', 'flow', 'board', 'git', 'hcl', 'regex', 'ebnf', 'files']
+            enumerations = ['uml', 'bpm', 'wire', 'dot', 'ditaa', 'salt', 'math', 'latex', 'chart', 'gantt', 'mindmap', 'wbs', 'yaml', 'creole', 'json', 'flow', 'board', 'git', 'hcl', 'regex', 'ebnf', 'files']
             if value not in enumerations:
                 lineno = self.gds_get_node_lineno_()
                 self.gds_collector_.add_message('Value "%(value)s"%(lineno)s does not match xsd enumeration restriction on DoxPlantumlEngine' % {"value" : encode_str_2_3(value), "lineno": lineno} )

doc/commands.dox

@@ -3588,7 +3588,7 @@ class Receiver
 
   Not all diagrams can be created with the PlantUML `@startuml` command but need another
   PlantUML `@start...` command. This will look like `@start<engine>` where currently supported are
-  the following `<engine>`s: `uml`, `bpm`, `wire`, `dot`, `ditaa`, `salt`, `math`, `latex`,
+  the following `<engine>`s: `uml`, `bpm`, `wire`, `dot`, `ditaa`, `salt`, `math`, `latex`, 'chart',
   `gantt`, `mindmap`, `wbs`, `yaml`, `creole`, `json`, `flow`, `board`, `git`, `hcl`, `regex`, `ebnf`,
   `files`, `chen` and `chronology`.
   By default the `<engine>` is `uml`. The `<engine>` can be specified as an option.

src/docnode.cpp

@@ -72,7 +72,7 @@ static const StringUnorderedSet g_plantumlEngine {
   "salt", "math", "latex", "gantt", "mindmap",
   "wbs", "yaml", "creole", "json", "flow",
   "board", "git", "hcl", "regex", "ebnf",
-  "files", "chen", "chronology"
+  "files", "chen", "chronology", "chart"
 };
 
 //---------------------------------------------------------------------------

templates/xml/compound.xsd

@@ -1196,6 +1196,7 @@
       <xsd:enumeration value="salt"/>
       <xsd:enumeration value="math"/>
       <xsd:enumeration value="latex"/>
+      <xsd:enumeration value="chart"/>
       <xsd:enumeration value="gantt"/>
       <xsd:enumeration value="mindmap"/>
       <xsd:enumeration value="wbs"/>