Incorrect DTD for wstcref-Files

### Apache NetBeans version

Apache NetBeans 23

### What happened

The DTD for wstcref-Files of version 2.2 (https://github.com/apache/netbeans/blob/master/platform/core.windows/src/org/netbeans/core/windows/resources/tc-ref2_2.dtd) contains two errors:

1. The previousMode tag is required by the DTD, but not in the application runtime

2. The previousMode attribute list is not formed well according to the W3C Recommendation (see https://www.w3.org/TR/2006/REC-xml11-20060816/): The name attribute has no so called Attribute Default (#REQUIRED, #IMPLIED or definition)

### Language / Project Type / NetBeans Component

NetBeans Platform DTDs

### How to reproduce

To reproduce the first problem mentioned above simple try to validate the persistance files generated by the NetBeans platform (can be found in the ProgramData folder), e.g.:
```

```
As you can see, even the generated files do not contain a previousMode-tag, cause it is only needed for docking/sliding operations.

The second problem occurs if you want to validate any wstcref-File of version 2.2 using the ant xmlvalidate task, cause it cannot parse the DTD referenced due to the wong formed attribute list of the previousMode tag.

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

No / Don't know

### Operating System

Windows 10

### JDK

17

### Apache NetBeans packaging

Apache NetBeans platform

### Anything else

_No response_

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

Yes

Start with platform/core.windows/src/org/netbeans/core/windows/resources/tc-ref2_2.dtd, linked in the issue, and compare its previousMode declaration with the generated tc-ref version 2.2 example. Validate the corrected DTD and sample persistence file with the ant xmlvalidate task; done means the generated file validates and the DTD parses according to the XML recommendation.

Written by the indexing model from the issue text.