[PHP] Accessing undeclared/inaccessible class constant must produce error

### Apache NetBeans version

Apache NetBeans 18

### What happened

Accessing undeclared/inaccessible class constant must produce error.

### How to reproduce

```php
fnInstance();
myFunc($ins1);

$ins2 = new MyClass2;
$ins2::fnStatic();
$ins2->fnInstance();
```

### Did this work correctly in an earlier version?

No / Don't know

### Operating System

Windows 10

### JDK

Java: 14.0.1; Java HotSpot(TM) 64-Bit Server VM 14.0.1+7 Runtime: Java(TM) SE Runtime Environment 14.0.1+7

### Apache NetBeans packaging

Apache NetBeans binary zip

### Anything else

_No response_

### Are you willing to submit a pull request?

No

Start by reproducing the supplied PHP example in Apache NetBeans 18 and observe which class-constant accesses receive diagnostics. Trace the PHP editor's handling of declared, inaccessible, and undefined constants; done means invalid accesses are reported while the marked valid accesses are not.

Written by the indexing model from the issue text.