Add GizmosShowOnGameViewAttribute

[nowsprinting]

GizmosShowOnGameViewAttribute is an NUnit test attribute class to show/hide Gizmos on GameView during the test running.

This attribute can attached to test method only.
Can be used with sync Test, async Test, and UnityTest.

Usage:

using NUnit.Framework;
using TestHelper.Attributes;

[TestFixture]
public class MyTestClass
{
    [Test]
    [GizmosShowOnGameView(true)]
    public void MyTestMethod()
    {
        // Show Gizmos on GameView.
    }
}

Note
In batchmode, open GameView window.

[github-actions]

Code Metrics Report

	master (d30a554)	#37 (46d4195)	+/-
Coverage	58.3%	63.2%	+4.9%
Code to Test Ratio	1:1.9	1:1.9	-0.0
Test Execution Time	4m57s	4m18s	-39s

Details

  |                     | master (d30a554) | #37 (46d4195) |  +/-  |
  |---------------------|------------------|---------------|-------|
+ | Coverage            |            58.3% |         63.2% | +4.9% |
  |   Files             |               22 |            23 |    +1 |
  |   Lines             |              482 |           527 |   +45 |
+ |   Covered           |              281 |           333 |   +52 |
- | Code to Test Ratio  |            1:1.9 |         1:1.9 |  -0.0 |
  |   Code              |              499 |           542 |   +43 |
+ |   Test              |              938 |          1013 |   +75 |
+ | Test Execution Time |            4m57s |         4m18s |  -39s |

Code coverage of files in pull request scope (40.2% → 65.9%)

Files	Coverage	+/-
Runtime/Attributes/GizmosShowOnGameViewAttribute.cs	100.0%	+100.0%
Runtime/Attributes/TakeScreenshotAttribute.cs	100.0%	0.0%
RuntimeInternals/GameViewControlHelper.cs	47.3%	+11.7%
RuntimeInternals/Wrappers/UnityEditor/GameViewWrapper.cs	60.0%	+39.3%

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Reported by octocov