Correct horizontal coordinates in viewport overflow test (#8456)

When resizing the buffer in the `SetConsoleScreenBufferSize` and
`SetConsoleScreenBufferInfoEx` APIs, we have tests in place to make sure
that the resize doesn't result in the viewport extending past the bottom
or right of the buffer (since that can eventually result in exceptions
being thrown). Unfortunately these tests were using the wrong X
coordinate, so they failed to detect an overflow along the horizontal
axis. This PR corrects that mistake.

PR #8309 was where the overflow detection was initially added.

The original code was using the `Viewport::EndExclusive` method to
determine the extent of the viewport, mistakenly thinking that it
returned the bottom right coordinates (it actually returns the left
coordinate). So I've now added a `BottomRightExclusive` method to the
`Viewport` class, that actually does return the coordinates we need, and
have updated the overflow tests to use that method instead.

## Validation Steps Performed
I've manually confirmed that the test case is issue #8453 is no longer
throwing an exception. 

Closes #8453

src/host/getset.cpp

@@ -528,7 +528,7 @@ void ApiRoutines::GetLargestConsoleWindowSizeImpl(const SCREEN_INFORMATION& cont
         }
 
         // Make sure the viewport doesn't now overflow the buffer dimensions.
-        auto overflow = screenInfo.GetViewport().EndExclusive() - screenInfo.GetBufferSize().Dimensions();
+        auto overflow = screenInfo.GetViewport().BottomRightExclusive() - screenInfo.GetBufferSize().Dimensions();
         if (overflow.X > 0 || overflow.Y > 0)
         {
             overflow = { std::max<SHORT>(overflow.X, 0), std::max<SHORT>(overflow.Y, 0) };
@@ -638,7 +638,7 @@ void ApiRoutines::GetLargestConsoleWindowSizeImpl(const SCREEN_INFORMATION& cont
         // Note that it also doesn't set cursor position.
 
         // However, we do need to make sure the viewport doesn't now overflow the buffer dimensions.
-        auto overflow = context.GetViewport().EndExclusive() - context.GetBufferSize().Dimensions();
+        auto overflow = context.GetViewport().BottomRightExclusive() - context.GetBufferSize().Dimensions();
         if (overflow.X > 0 || overflow.Y > 0)
         {
             overflow = { std::max<SHORT>(overflow.X, 0), std::max<SHORT>(overflow.Y, 0) };

src/types/inc/viewport.hpp

@@ -57,6 +57,7 @@ namespace Microsoft::Console::Types
         SHORT Height() const noexcept;
         SHORT Width() const noexcept;
         COORD Origin() const noexcept;
+        COORD BottomRightExclusive() const noexcept;
         COORD EndExclusive() const noexcept;
         COORD Dimensions() const noexcept;
 

src/types/viewport.cpp

@@ -137,6 +137,17 @@ COORD Viewport::Origin() const noexcept
     return { Left(), Top() };
 }
 
+// Method Description:
+// - Get a coord representing the bottom right of the viewport in exclusive terms.
+// Arguments:
+// - <none>
+// Return Value:
+// - the exclusive bottom right coordinates of this viewport.
+COORD Viewport::BottomRightExclusive() const noexcept
+{
+    return { RightExclusive(), BottomExclusive() };
+}
+
 // Method Description:
 // - For Accessibility, get a COORD representing the end of this viewport in exclusive terms.
 // - This is needed to represent an exclusive endpoint in UiaTextRange that includes the last