Add chained method calls to Dialect for fluent code navigation

[nikomatsakis]

Objective

Add support for chained method calls in Dialect to enable more expressive and readable code navigation queries.

Problem

Current Dialect syntax is limited to simple function calls, making complex location queries verbose or impossible:

// Current - limited expressiveness
findDefinition(`User`)
search(`*.rs`, `TODO:`)

Solution

Implement chained method calls for fluent API-style navigation:

// Proposed - fluent and expressive
findDefinition(`User`).methods().named('validate')
search(`*.rs`, `TODO:`).limit(5).inFile('auth')
findReferences(`validate_token`).filter(f => f.path.includes('test')).first()

Implementation Ideas

Core Method Categories

Filtering methods:

• .filter(predicate) - Filter results by condition
• .named(pattern) - Filter by name matching
• .inFile(pattern) - Filter by file path
• .inDirectory(path) - Filter by directory

Selection methods:

• .first() - Take first result
• .last() - Take last result
• .limit(n) - Take first n results
• .at(index) - Take result at index

Symbol-specific methods:

• .methods() - Get methods of a class/struct
• .fields() - Get fields of a class/struct
• .implementations() - Get trait implementations
• .usages() - Get usage sites

Location methods:

• .line(n) - Move to specific line in same file
• .range(start, end) - Expand to line range

Example Use Cases

Find specific method in class:

findDefinition(`TokenValidator`).methods().named('validate')

Find TODO comments in auth module:

search(`src/auth/**/*.rs`, `TODO:`).limit(10)

Find test usages of a function:

findReferences(`validate_token`).inDirectory('tests').first()

Find struct fields:

findDefinition(`User`).fields().named('email')

Benefits

• More readable - Natural language-like queries
• More powerful - Complex filtering and selection
• Better UX - Easier for LLMs to generate correct expressions
• Extensible - Easy to add new methods over time

Implementation Notes

• Maintain backward compatibility with current simple function calls
• Consider lazy evaluation for performance
• Add comprehensive error messages for invalid chains
• Document method availability per result type

Context

This enhancement supports the new markdown+XML walkthrough format (#30) by making location expressions more natural and powerful for AI assistants to generate.