feat(emitter): add support for HCL expression AST nodes in module calls

[glucaci]

This pull request adds support for setting Terraform module input variables using HCL AST expressions, enabling more flexible and accurate emission of complex, multi-line HCL values. It introduces a new overload for ModuleCallBuilder.Set that accepts an HclExpression, updates the HCL emission logic to handle multi-line values with correct indentation, and exposes a utility for emitting any HCL expression as a canonical string. Comprehensive tests and documentation are included to demonstrate and validate these new capabilities.

Core API Enhancements:

• Added a new overload Set(string name, HclExpression expression) to ModuleCallBuilder, allowing variables to be set using HCL AST nodes for complex or multi-line values. [1] [2]
• Exposed a new public static method ModuleCallEmitter.EmitExpression(HclExpression expression) to emit any HCL AST node as a canonical HCL string. [1] [2]

HCL Emission Improvements:

• Improved the emission of multi-line HCL values in module blocks: continuation lines are now properly indented to align under the first value character, ensuring correct and readable output for nested objects, tuples, and for-expressions.

Testing:

• Added extensive unit tests for the new Set(HclExpression) overload and for the EmitExpression method, covering variable references, function calls, literals, objects, tuples, for-expressions, and multi-line formatting. [1] [2]

Documentation:

• Updated and expanded the documentation in terraformdotnet.md to describe the new features, including usage examples and explanations for setting variables from HCL AST expressions and emitting expressions standalone.