Mark occurrences of enum constructors

### Description

Unlike constructors of regular classes, the "mark occurrences" mechanism doesn't mark usages of enum constructors. Example:

```java
class Example
{
@SuppressWarnings("unused")
static class Class
{
static final Class A = new Class();
static final Class B = new Class();
static final Class C = new Class();

Class() { }
}

enum Enum
{
A(),
B(),
C();

Enum() { }
}
}
```
Place the cursor on the `Class()` constructor => The three `new Class()` invocations are highlighted and shown in the right-hand editor sidebar.
Place the cursor on the `Enum()` constructor => The three invocations from the enum constants are not highlighted.

### Use case/motivation

In large enum classes, where the enum constants have implementations that may span many lines, an/or where the constants may have extensive Javadoc comments, highlighting the constants (which effectively are constructor invocations) would be useful.

### Related issues

#8985

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

No

Start by locating NetBeans' Java editor implementation of the “mark occurrences” mechanism and its handling of constructor references. Reproduce the example with the cursor on Class() and Enum(), then trace how enum constants are represented. Done means enum constructor occurrences are highlighted consistently with regular class constructor invocations.

Written by the indexing model from the issue text.