Re-use existing .refitter file if it already exists

[christianhelle]

PR Classification

This pull request ensures that the existing .refitter file is not overwritten when the user runs the refitter command. It also updates the serialization method to use System.Text.Json.JsonSerializer instead of JsonConvert.SerializeObject.

PR Summary

The pull request modifies the RefitterCodeGenerator.cs file to improve the handling of RefitGeneratorSettings and updates the serialization method.

• RefitterCodeGenerator.cs: Updated using directives, added logic to check for a .refitter file before deserializing settings, and moved the serialization of settings to an else block.
• RefitterCodeGenerator.cs: Switched from JsonConvert.SerializeObject to a new Serialize method for creating the DependencyContext.
• RefitterCodeGenerator.cs: Added a new private Serialize method for serializing RefitGeneratorSettings with System.Text.Json.JsonSerializer.

[sonarcloud[bot]]

Quality Gate failed

Failed conditions
0.0% Coverage on New Code (required ≥ 80%)

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