Java pacmak breaks if docstring contains `\u` character string

## :bug: Bug Report

### Affected Languages
- [ ] `TypeScript` or `Javascript`
- [ ] `Python`
- [x] `Java`
- [ ] .NET (`C#`, `F#`, ...)
- [ ] `Go`

### General Information
* **JSII Version:** 1.50.0

### What is the problem?

If the docstring for an element contains the string `\u`, the Java build fails:

```
#STDOUT> [ERROR] /tmp/npm-pack6Fz26z/_aws-cdk_aws-lex/src/main/java/software/amazon/awscdk/services/lex/CfnBot.java:[11584,39] illegal unicode escape
#STDOUT> [ERROR] /tmp/npm-pack6Fz26z/_aws-cdk_aws-lex/src/main/java/software/amazon/awscdk/services/lex/CfnBot.java:[13,1] illegal unicode escape
#STDOUT> [ERROR] /tmp/npm-pack6Fz26z/_aws-cdk_aws-lex/src/main/java/software/amazon/awscdk/services/lex/CfnBot.java:[11621,58] illegal unicode escape
#STDOUT> [ERROR] /tmp/npm-pack6Fz26z/_aws-cdk_aws-lex/src/main/java/software/amazon/awscdk/services/lex/CfnBot.java:[17,32] illegal unicode escape
```

Code in question:

```java
/**
* A regular expression used to validate the value of a slot.
*

* Use a standard regular expression. Amazon Lex supports the following characters in the regular expression:
*

*

*
• A-Z, a-z
*
• 0-9

*
• Unicode characters ("\u")

*

*

* Represent Unicode characters with four digits, for example "]u0041" or "\u005A".
*

* The following regular expression operators are not supported:
*

*

*
• Infinite repeaters: *, +, or {x,} with no upper bound

*
• Wild card (.)

*

*/
@software.amazon.jsii.Stability(software.amazon.jsii.Stability.Level.Stable)
@org.jetbrains.annotations.NotNull java.lang.String getPattern();
```

The correct rendering should be `\\u`.

Start by tracing the Java pacmak rendering path for docstrings and reproduce the failure with a docstring containing the literal `\u`. Compare the generated Java documentation with the expected escaped `\\u` rendering, then run the relevant Java generation or packaging tests if present; done means the generated Java build succeeds for this case.

Written by the indexing model from the issue text.