Fix OperandReferenceAnalyzer to recognize all undefined data types

[0xFE4415]

Use Undefined.isUndefined(dt) instead of dt instanceof Undefined, so that multi-byte undefined types are detected as undefined.
The instanceof check missed some variants of undefined causing the analyzer to treat them as defined and skip creating pointer references on them.

[0xFE4415]

Minimized reproduction:

gcc 1.c -o a.out
source build/venv/bin/activate # I used: ./gradlew prepPyGhidra
python run_1c.py a.out

Expected Result (Slot 1 is a pointer):

'c' at 00403020, pointer size = 8
  slot 0 00403020: dt=undefined len=1 pointer=False
  slot 1 00403028: dt=pointer len=8 pointer=True
...

Actual Result (Slot 1 is undefined):

'c' at 00403020, pointer size = 8
  slot 0 00403020: dt=undefined1[16] len=16 pointer=False
  slot 1 00403028: dt=undefined1[16] len=16 pointer=False
...

Here is the compiled binary: (a.out.zip).

[0xFE4415]

Disclosure: I added tests with help of an AI assistant. I also manually verified that UndefinedArray test is, in fact, a regression test.

[emteere]

Looks good. Thanks for the PR