Fix the Alternate Scroll Mode when DECCKM enabled (#5081)

## Summary of the Pull Request

If the _Alternate Scroll Mode_ is enabled, the terminal generates up/down keystrokes when the mouse wheel is scrolled. However, the expected escape sequences for those keys are dependent on the state of the _Cursor Keys Mode_ ( `DECCKM`), but we haven't taken that into account. This PR updates the alternate scroll implementation to make sure the appropriate sequences are sent for both `DECCKM` modes.

## References

#3321

## PR Checklist
* [ ] Closes #xxx
* [x] CLA signed. If not, go over [here](https://cla.opensource.microsoft.com/microsoft/Terminal) and sign the CLA
* [x] Tests added/passed
* [ ] Requires documentation to be updated
* [ ] I've discussed this with core contributors already. If not checked, I'm ready to accept this work might be rejected in favor of a different grand plan. Issue number where discussion took place: #xxx

## Detailed Description of the Pull Request / Additional comments

I've simply added a condition in the `TerminalInput::_SendAlternateScroll` method to send a different pair of sequences dependent on the state of `_cursorApplicationMode`  flag.

## Validation Steps Performed

Manually tested in VIM (although that required me enabling the _Alternate Scroll Mode_ myself first). Also added a new unit test in `MouseInputTest` to confirm the correct sequences were generated for both `DECCKM` modes.

src/terminal/adapter/ut_adapter/MouseInputTest.cpp

@@ -593,4 +593,44 @@ class MouseInputTest
                              NoThrowString().Format(L"(x,y)=(%d,%d)", Coord.X, Coord.Y));
         }
     }
+
+    TEST_METHOD(AlternateScrollModeTests)
+    {
+        Log::Comment(L"Starting test...");
+        std::unique_ptr<TerminalInput> mouseInput = std::make_unique<TerminalInput>(s_MouseInputTestCallback);
+        const short noModifierKeys = 0;
+
+        Log::Comment(L"Enable alternate scroll mode in the alt screen buffer");
+        mouseInput->UseAlternateScreenBuffer();
+        mouseInput->EnableAlternateScroll(true);
+
+        Log::Comment(L"Test mouse wheel scrolling up");
+        s_pwszInputExpected = L"\x1B[A";
+        VERIFY_IS_TRUE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, 1));
+
+        Log::Comment(L"Test mouse wheel scrolling down");
+        s_pwszInputExpected = L"\x1B[B";
+        VERIFY_IS_TRUE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, -1));
+
+        Log::Comment(L"Enable cursor keys mode");
+        mouseInput->ChangeCursorKeysMode(true);
+
+        Log::Comment(L"Test mouse wheel scrolling up");
+        s_pwszInputExpected = L"\x1BOA";
+        VERIFY_IS_TRUE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, 1));
+
+        Log::Comment(L"Test mouse wheel scrolling down");
+        s_pwszInputExpected = L"\x1BOB";
+        VERIFY_IS_TRUE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, -1));
+
+        Log::Comment(L"Confirm no effect when scroll mode is disabled");
+        mouseInput->UseAlternateScreenBuffer();
+        mouseInput->EnableAlternateScroll(false);
+        VERIFY_IS_FALSE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, 1));
+
+        Log::Comment(L"Confirm no effect when using the main buffer");
+        mouseInput->UseMainScreenBuffer();
+        mouseInput->EnableAlternateScroll(true);
+        VERIFY_IS_FALSE(mouseInput->HandleMouse({ 0, 0 }, WM_MOUSEWHEEL, noModifierKeys, 1));
+    }
 };

src/terminal/input/mouseInput.cpp

@@ -19,6 +19,8 @@ static constexpr short KeyPressed{ gsl::narrow_cast<short>(0x8000) };
 // Alternate scroll sequences
 static constexpr std::wstring_view CursorUpSequence{ L"\x1b[A" };
 static constexpr std::wstring_view CursorDownSequence{ L"\x1b[B" };
+static constexpr std::wstring_view ApplicationUpSequence{ L"\x1bOA" };
+static constexpr std::wstring_view ApplicationDownSequence{ L"\x1bOB" };
 
 // Routine Description:
 // - Determines if the input windows message code describes a button event
@@ -523,11 +525,11 @@ bool TerminalInput::_SendAlternateScroll(const short delta) const noexcept
 {
     if (delta > 0)
     {
-        _SendInputSequence(CursorUpSequence);
+        _SendInputSequence(_cursorApplicationMode ? ApplicationUpSequence : CursorUpSequence);
     }
     else
     {
-        _SendInputSequence(CursorDownSequence);
+        _SendInputSequence(_cursorApplicationMode ? ApplicationDownSequence : CursorDownSequence);
     }
     return true;
 }