Copy multiline string (not text blocks)

### Description

It would be nice if I could copy the content of a multiline string (a String consisting of multiple code lines of concatenated strings, not a Java 15 Text Block) directly. I.e:

```java
String s = "This " +
"string spans " +
"multiple code lines.";
```

I would want a feature so I can copy "This string spans multiple code lines." directly, without removing manually the `"` and `+` characters.

### Use case/motivation

_No response_

### Related issues

_No response_

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

No

The issue names no implementation files or tests. Start by locating NetBeans' Java editor copy handling and string-literal parsing, then check existing editor copy tests; done means copying a concatenated multiline Java string produces its combined content without quotes or plus characters while preserving ordinary copy behavior.

Written by the indexing model from the issue text.