Detect enclosing function for JavaScript

[xaldama]

Summary

• Implements enclosing function detection for JavaScript (FQN format: ClassName.methodName for class methods, functionName for top-level functions and variable-assigned arrow/anonymous functions)
• Named function expressions use the explicit function name; anonymous functions assigned to a variable use the variable name

Test plan

• Unit tests in javascript/methods.rs cover function declarations, class methods, arrow functions, anonymous functions, named function expressions, and unassigned anonymous functions

[datadog-prod-us1-3]

🎯 Code Coverage (details)
• Patch Coverage: 92.81%
• Overall Coverage: 85.13% (+0.05%)

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