[Conhost] Fix off-by-1 error when copying and coloring selections (#19259)

## Summary of the Pull Request
Fixes a bug where copying and coloring selected text would be off by
one. This was introduced in #18106 when selection was updated to be
stored as an exclusive range. `Selection::_RegenerateSelectionSpans()`
was updated then, but copying text and coloring selection didn't rely on
selection spans.

Copying text relies on `GetSelectionAnchors()`. This function has now
been updated to increment the bottom-right point of the selection. This
way, `GetTextSpans()` operates on the expected _exclusive_ range.

Coloring selection relies on `TextBuffer::SearchText()`,
`TextBuffer::GetTextRects` and `GetSelectionSpans()`. Both
`Selection::ColorSelection()` were updated to use `rect` over
`inclusive_rect` to emphasize that they are exclusive ranges. Converting
between the two improves clarity and fixes the bug.

## References and Relevant Issues
Introduced in #18106 

## Validation Steps Performed
Copying text works in the following scenarios:
✅ single line, left-to-right and right-to-left
✅ multi-line, diagonal directions
✅ block selection

Coloring text works in the following scenarios:
✅ctrl+# --> color instance
✅ctrl+shift+# --> color all instances

Closes #19053

src/host/selection.cpp

@@ -428,9 +428,9 @@ void Selection::ClearSelection(const bool fStartingNewSelection)
 // - This does not validate whether there is a valid selection right now or not.
 //   It is assumed to already be in a proper selecting state and the given rectangle should be highlighted with the given color unconditionally.
 // Arguments:
-// - psrRect - Rectangular area to fill with color
+// - psrRect - Rectangular area to fill with color (exclusive)
 // - attr - The color attributes to apply
-void Selection::ColorSelection(const til::inclusive_rect& srRect, const TextAttribute attr)
+void Selection::ColorSelection(const til::rect& srRect, const TextAttribute attr)
 {
     auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
 
@@ -438,8 +438,8 @@ void Selection::ColorSelection(const til::inclusive_rect& srRect, const TextAttr
     auto& screenInfo = gci.GetActiveOutputBuffer();
 
     til::point coordTargetSize;
-    coordTargetSize.x = CalcWindowSizeX(srRect);
-    coordTargetSize.y = CalcWindowSizeY(srRect);
+    coordTargetSize.x = srRect.width();
+    coordTargetSize.y = srRect.height();
 
     til::point coordTarget;
     coordTarget.x = srRect.left;
@@ -475,9 +475,9 @@ void Selection::ColorSelection(const til::point coordSelectionStart, const til::
         const auto& screenInfo = gci.GetActiveOutputBuffer();
 
         const auto rectangles = screenInfo.GetTextBuffer().GetTextRects(coordSelectionStart, coordSelectionEnd, false, true);
-        for (const auto& rect : rectangles)
+        for (const auto& inclusiveRect : rectangles)
         {
-            ColorSelection(rect, attr);
+            ColorSelection(til::rect{ inclusiveRect }, attr);
         }
     }
     CATCH_LOG();

src/host/selection.hpp

@@ -58,7 +58,7 @@ public:
 
     void ClearSelection();
     void ClearSelection(const bool fStartingNewSelection);
-    void ColorSelection(const til::inclusive_rect& srRect, const TextAttribute attr);
+    void ColorSelection(const til::rect& srRect, const TextAttribute attr);
     void ColorSelection(const til::point coordSelectionStart, const til::point coordSelectionEnd, const TextAttribute attr);
 
     // delete these or we can accidentally get copies of the singleton

src/host/selectionInput.cpp

@@ -698,7 +698,7 @@ bool Selection::_HandleColorSelection(const INPUT_KEY_INFO* const pInputKeyInfo)
             for (auto&& sp : selection)
             {
                 sp.iterate_rows(textBuffer.GetSize().Width(), [&](til::CoordType row, til::CoordType beg, til::CoordType end) {
-                    ColorSelection({ beg, row, end, row }, selectionAttr);
+                    ColorSelection({ beg, row, end, row + 1 }, selectionAttr);
                 });
             }
             ClearSelection();

src/host/selectionState.cpp

@@ -220,6 +220,23 @@ std::pair<til::point, til::point> Selection::GetSelectionAnchors() const noexcep
     endSelectionAnchor.x = (_d->coordSelectionAnchor.x == _d->srSelectionRect.left) ? _d->srSelectionRect.right : _d->srSelectionRect.left;
     endSelectionAnchor.y = (_d->coordSelectionAnchor.y == _d->srSelectionRect.top) ? _d->srSelectionRect.bottom : _d->srSelectionRect.top;
 
+    // GH #18106: Conhost and Terminal share most of the selection code.
+    //    Both now store the selection data as a half-open range [start, end),
+    //     where "end" is the bottom-right-most point.
+    // Conhost operates as an inclusive range, so we need to adjust the "end" endpoint by incrementing it by one.
+    const auto& gci = ServiceLocator::LocateGlobals().getConsoleInformation();
+    const auto& bufferSize = gci.GetActiveOutputBuffer().GetTextBuffer().GetSize();
+    if (IsLineSelection())
+    {
+        // General comparison for line selection.
+        bufferSize.IncrementInExclusiveBounds(startSelectionAnchor <= endSelectionAnchor ? endSelectionAnchor : startSelectionAnchor);
+    }
+    else
+    {
+        // Compare x-values when we're in block selection!
+        bufferSize.IncrementInExclusiveBounds(startSelectionAnchor.x <= endSelectionAnchor.x ? endSelectionAnchor : startSelectionAnchor);
+    }
+
     if (startSelectionAnchor > endSelectionAnchor)
     {
         return { endSelectionAnchor, startSelectionAnchor };