Add syntax highlighting for project symbol search

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Summary

Implements label_for_symbol to provide syntax-highlighted labels in the project symbol picker (cmd-t). Currently, Java symbols appear as plain grey text with no highlighting, unlike Rust and other languages that already implement this.

Ref: zed-industries/zed#36383, zed-industries/zed#37176

Changes

• Add label_for_symbol to the Extension for Java impl
• Import Symbol and SymbolKind from the extension API
• Generate Tree-sitter-parseable code snippets for each symbol kind so the Java grammar produces correct AST nodes and syntax highlighting
• Wrap member-level constructs (methods, fields, constructors) inside class _ { } since Java's Tree-sitter grammar requires class context for these declarations
• Display symbols in Java declaration order (type before name): void doWork(String, int), String fieldName
• Show keyword prefixes for type declarations: class, interface, enum, package

Supported symbol kinds

Kind	Display example	Tree-sitter context
Class	class MyClass	class MyClass {}
Interface	interface Runnable	interface Runnable {}
Enum	enum Status	enum Status {}
Constructor	MyClass(String, int)	class MyClass { MyClass() {} }
Method	void doWork(String, int)	class _ { void doWork() {} }
Field	String name	class _ { String name; }
Constant	MAX_SIZE	class _ { static final int MAX_SIZE; }
EnumMember	ACTIVE	enum _ { ACTIVE }
Variable	count	class _ { int count; }
Package	package com.example	package com.example;

Screenshot:

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