Correcting error handling in .NET finding of elements

This commit removes the `IllegalLocatorException`. This exception was only
thrown when finding by class name where the class name contained
whitespace. It is redundant, and now `InvalidSelectorException` is thrown
in its place. This commit also corrects the element finding tests to
expect the proper `InvalidSelectorException` when finding by tag name,
where the tag name provided is an empty string.

Author: jimevans

dotnet/src/webdriver/IllegalLocatorException.cs

@@ -180,7 +180,6 @@
     <Compile Include="IHasInputDevices.cs" />
     <Compile Include="IJavascriptExecutor.cs" />
     <Compile Include="IKeyboard.cs" />
-    <Compile Include="IllegalLocatorException.cs" />
     <Compile Include="ILocatable.cs" />
     <Compile Include="IMouse.cs" />
     <Compile Include="INavigation.cs" />

dotnet/src/webdriver/WebDriver.csproj

@@ -189,14 +189,14 @@ public void ShouldNotBeAbleToLocateByTagNameMultipleElementsThatDoNotExist()
         public void FindingASingleElementByEmptyTagNameShouldThrow()
         {
             driver.Url = formsPage;
-            Assert.Throws<NoSuchElementException>(() => driver.FindElement(By.TagName("")));
+            Assert.Throws<InvalidSelectorException>(() => driver.FindElement(By.TagName("")));
         }
 
         [Test]
         public void FindingMultipleElementsByEmptyTagNameShouldThrow()
         {
             driver.Url = formsPage;
-            Assert.Throws<NoSuchElementException>(() => driver.FindElements(By.TagName("")));;
+            Assert.Throws<InvalidSelectorException>(() => driver.FindElements(By.TagName("")));;
         }
 
         [Test]
@@ -305,7 +305,7 @@ public void FindingMultipleElementsByEmptyClassNameShouldThrow()
         public void FindingASingleElementByCompoundClassNameShouldThrow()
         {
             driver.Url = xhtmlTestPage;
-            Assert.Throws<IllegalLocatorException>(() => driver.FindElement(By.ClassName("a b")));
+            Assert.Throws<InvalidSelectorException>(() => driver.FindElement(By.ClassName("a b")));
         }
 
         [Test]
@@ -314,7 +314,7 @@ public void FindingASingleElementByCompoundClassNameShouldThrow()
         public void FindingMultipleElementsByCompoundClassNameShouldThrow()
         {
             driver.Url = xhtmlTestPage;
-            Assert.Throws<IllegalLocatorException>(() => driver.FindElements(By.ClassName("a b")));
+            Assert.Throws<InvalidSelectorException>(() => driver.FindElements(By.ClassName("a b")));
         }
 
         [Test]