Add ECS0008 use the null conditional operator for event invocations

[rjmurillo]

This pull request introduces a new analyzer rule, ECS0008, which is designed to enforce the use of the null-conditional operator when invoking event handlers in C#. This practice helps prevent potential NullReferenceExceptions, improving the safety and robustness of the code.

Key Features:

• Detection of Potential Violations: The rule identifies patterns where an event handler is invoked without using the null-conditional operator (?.Invoke), such as direct invocations or invocations within an if statement checking for null.
• Automatic Code Fixes: The code fix provider automatically replaces the identified pattern with the null-conditional operator, ensuring that the event handler is only invoked when it has subscribers.
• Comprehensive Coverage: The rule handles cases where the event handler is checked directly and cases where it is first assigned to a local variable.

Example Violation:

public class EventSource
{
    private EventHandler<int> Updated;
    private int counter;

    public void RaiseUpdates()
    {
        counter++;
        if (Updated != null)
            Updated(this, counter);
    }
}

Fixed code:

public class EventSource
{
    private EventHandler<int> Updated;
    private int counter;

    public void RaiseUpdates()
    {
        counter++;
        Updated?.Invoke(this, counter);
    }
}

[codacy-production[bot]]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
:white_check_mark: +2.62% (target: -1.00%)	:white_check_mark: 95.62%

Coverage variation details

| | Coverable lines | Covered lines | Coverage | | ------------- | ------------- | ------------- | ------------- | | Common ancestor commit (a98a3388b9638d1b104e8df36501a3d80436d42a) | 531 | 440 | 82.86% | | | Head commit (0bec5600e930bdd94c1ada38c4b8e18a5249e76d) | 668 (+137) | 571 (+131) | 85.48% (**+2.62%**) | **Coverage variation** is the difference between the coverage for the head and common ancestor commits of the pull request branch: ` - `

Diff coverage details

| | Coverable lines | Covered lines | Diff coverage | | ------------- | ------------- | ------------- | ------------- | | Pull request (#48) | 137 | 131 | **95.62%** | **Diff coverage** is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: `/ * 100%`

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