Adds Import/L5xParser.cs that consumes Studio 5000 L5X (XML) controller
exports via System.Xml.XPath and produces the same L5kDocument bundle as
L5kParser, so L5kIngest handles both formats interchangeably.
- Controller-scope and program-scope <Tag> elements with Name, DataType,
TagType, ExternalAccess, AliasFor, and <Description> child.
- <DataType>/<Members>/<Member> with Hidden BOOL-host (ZZZZZZZZZZ*) skip.
- AddOnInstructionDefinitions surfaced as L5kDataType entries so AOI-typed
tags pick up a member layout the same way UDT-typed tags do; hidden
EnableIn/EnableOut parameters skipped. Full directional Input/Output/InOut
modelling stays deferred to PR 2.6.
AbCipDriverOptions gains parallel L5xImports collection (mirrors
L5kImports field-for-field). InitializeAsync funnels both through one
shared MergeImport helper that differs only in the parser delegate.
Tests: 8 L5X fixtures cover controller- and program-scope tags, alias skip,
UDT layout fan-out, AOI-typed tag, ZZZZZZZZZZ host skip, hidden AOI param
skip, missing-ExternalAccess default, and an empty-controller no-throw.
Closes#230
