Add support for CSI 18t (#15295)

Adds support for CSI 18t to report the buffer screen size in characters.

This pull request adds support for **CSI 18t**. When submitted to the
terminal, it will respond with **"\033[8;{A};{B}t"** where **A** is
equal to the **height** and **B** is equal to the **width** of the
screen buffer in the number of characters (not pixels).

## Validation Steps Performed
Manual tests against PowerShell 7 and ConHost.
Added adapterTest

Closes #13944

Author: michalnpl

src/terminal/adapter/DispatchTypes.hpp

@@ -467,6 +467,7 @@ namespace Microsoft::Console::VirtualTerminal::DispatchTypes
         IconifyWindow = 2,
         RefreshWindow = 7,
         ResizeWindowInCharacters = 8,
+        ReportTextSizeInCharacters = 18
     };
 
     enum class CursorStyle : VTInt

src/terminal/adapter/adaptDispatch.cpp

@@ -3058,6 +3058,9 @@ bool AdaptDispatch::WindowManipulation(const DispatchTypes::WindowManipulationTy
     case DispatchTypes::WindowManipulationType::ResizeWindowInCharacters:
         _api.ResizeWindow(parameter2.value_or(0), parameter1.value_or(0));
         return true;
+    case DispatchTypes::WindowManipulationType::ReportTextSizeInCharacters:
+        _api.ReturnResponse(fmt::format(FMT_COMPILE(L"\033[8;{};{}t"), _api.GetViewport().height(), _api.GetTextBuffer().GetSize().Width()));
+        return true;
     default:
         return false;
     }

src/terminal/adapter/ut_adapter/adapterTest.cpp

@@ -2852,6 +2852,14 @@ class AdapterTest
         _pDispatch->_macroBuffer = nullptr;
     }
 
+    TEST_METHOD(WindowManipulationTypeTests)
+    {
+        _testGetSet->PrepData();
+        _pDispatch->WindowManipulation(DispatchTypes::WindowManipulationType::ReportTextSizeInCharacters, NULL, NULL);
+        const std::wstring expectedResponse = fmt::format(L"\033[8;{};{}t", _testGetSet->GetViewport().height(), _testGetSet->GetTextBuffer().GetSize().Width());
+        _testGetSet->ValidateInputEvent(expectedResponse.c_str());
+    }
+
 private:
     TerminalInput _terminalInput{ nullptr };
     std::unique_ptr<TestGetSet> _testGetSet;