pfSense

ArrayGetExprRector support for variable and funccall array keys

Change how buildPathArgNode() generates an Arg node - as we introduce support
for more complicated expressions in array keys to be converted to string path
expressions, a simple implode() is no longer sufficient. The following changes
are introduced:

• buildPathStringNode() function added that aggregates successive string keys
  into a single delimited path String_ node
• buildPathStringEncapsedNode() function added that uses buildPathStringNode to
  generate EncapsedStringPart nodes, aggregating them along with successive
  Variables and String_s as parts in an Encapsed node, adding delimiters as
  appropriate to String_ parts
• buildPathEncapsedOrStringNode() function added that builds either a plain
  String_ or Encapsed node as appropriate from the consumed nodes
• buildPathConcatNode() function added which creates a string Concat node from
  the first node and second node in the list, aggregating the second node on
  into either a String_ or Encapsed node with helpers as appropriate
• appendDelimiter() and prependDelimiter() functions added that will prepend or
  append a delimiter to a String_ or to the appropriate part of an Encapsed
  node, creating an additional String_ part if necessary for it
• buildPathArgNode() is modified to generate a String_, Encapsed, or Concat
  root node as appropriate depending on the input nodes, and properly nest
  Concat nodes into a root Concat node until all input nodes have been consumed
  by helpers

With these changes additional tests are provided to validate the desired output
is generated for a number of cases, using the variable 'config' for reference
fixtures.