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]

Coverage summary from Codacy

See diff coverage on Codacy

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

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (a98a338)	531	440	82.86%
Head commit (0bec560)	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: <coverage of head commit> - <coverage of common ancestor commit>

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: <covered lines added or modified>/<coverable lines added or modified> * 100%

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