Center "c" compass point is missing from the grammar

[nheir]

It's not possible to specify c as compass for portPos

Example from https://forum.graphviz.org/t/port-pos-center/1899/2

digraph top {
    node[shape=none]
    i [label=<<TABLE CELLSPACING="5" CELLPADDING="4" BORDER="0" CELLBORDER="1">
    <TR>
      <TD port="am">top of the morning</TD>
    </TR>  
    <TR>
      <TD port="cow">cattle crossing</TD>
    </TR>  
    <TR>
      <TD>d</TD>
    </TR>  
    </TABLE>> ]
    
  j [label=<<TABLE CELLSPACING="5" CELLPADDING="4" BORDER="0" CELLBORDER="1">
    <TR>
      <TD port="pm">afternoon</TD>
    </TR>  
    <TR>
      <TD>d</TD>
    </TR>  
    </TABLE>> ]

    p -> i:am:c [headclip=false]
    j:pm:c -> i:cow:c [headclip=false tailclip=false]
}

The grammar may be the only thing to fix

graphviz-visual-editor/src/dotGrammar.pegjs

Line 154 in 4823bcd

= 'n'/'ne'/'e'/'se'/'s'/'sw'/'w'/'nw'