Avoid encoding VT via win32 input mode (#16407)

This changeset avoids re-encoding output from `AdaptDispatch`
via the win32-input-mode mechanism when VT input is enabled.
That is, an `AdaptDispatch` output like `\x1b[C` would otherwise
result in dozens of characters of input.

Related to #16343

## Validation Steps Performed
* Replace conhost with this
* Launch a Win32 application inside WSL
* ASCII keyboard inputs are represented as single `INPUT_RECORD`s ✅

src/host/inputBuffer.cpp

@@ -602,6 +602,27 @@ size_t InputBuffer::Write(const std::span<const INPUT_RECORD>& inEvents)
     }
 }
 
+void InputBuffer::WriteString(const std::wstring_view& text)
+try
+{
+    if (text.empty())
+    {
+        return;
+    }
+
+    const auto initiallyEmptyQueue = _storage.empty();
+
+    _writeString(text);
+
+    if (initiallyEmptyQueue && !_storage.empty())
+    {
+        ServiceLocator::LocateGlobals().hInputEvent.SetEvent();
+    }
+
+    WakeUpReadersWaitingForData();
+}
+CATCH_LOG()
+
 // This can be considered a "privileged" variant of Write() which allows FOCUS_EVENTs to generate focus VT sequences.
 // If we didn't do this, someone could write a FOCUS_EVENT_RECORD with WriteConsoleInput, exit without flushing the
 // input buffer and the next application will suddenly get a "\x1b[I" sequence in their input. See GH#13238.
@@ -828,21 +849,7 @@ void InputBuffer::_HandleTerminalInputCallback(const TerminalInput::StringType&
             return;
         }
 
-        for (const auto& wch : text)
-        {
-            if (wch == UNICODE_NULL)
-            {
-                // Convert null byte back to input event with proper control state
-                const auto zeroKey = OneCoreSafeVkKeyScanW(0);
-                uint32_t ctrlState = 0;
-                WI_SetFlagIf(ctrlState, SHIFT_PRESSED, WI_IsFlagSet(zeroKey, 0x100));
-                WI_SetFlagIf(ctrlState, LEFT_CTRL_PRESSED, WI_IsFlagSet(zeroKey, 0x200));
-                WI_SetFlagIf(ctrlState, LEFT_ALT_PRESSED, WI_IsFlagSet(zeroKey, 0x400));
-                _storage.push_back(SynthesizeKeyEvent(true, 1, LOBYTE(zeroKey), 0, wch, ctrlState));
-                continue;
-            }
-            _storage.push_back(SynthesizeKeyEvent(true, 1, 0, 0, wch, 0));
-        }
+        _writeString(text);
 
         if (!_vtInputShouldSuppress)
         {
@@ -856,6 +863,25 @@ void InputBuffer::_HandleTerminalInputCallback(const TerminalInput::StringType&
     }
 }
 
+void InputBuffer::_writeString(const std::wstring_view& text)
+{
+    for (const auto& wch : text)
+    {
+        if (wch == UNICODE_NULL)
+        {
+            // Convert null byte back to input event with proper control state
+            const auto zeroKey = OneCoreSafeVkKeyScanW(0);
+            uint32_t ctrlState = 0;
+            WI_SetFlagIf(ctrlState, SHIFT_PRESSED, WI_IsFlagSet(zeroKey, 0x100));
+            WI_SetFlagIf(ctrlState, LEFT_CTRL_PRESSED, WI_IsFlagSet(zeroKey, 0x200));
+            WI_SetFlagIf(ctrlState, LEFT_ALT_PRESSED, WI_IsFlagSet(zeroKey, 0x400));
+            _storage.push_back(SynthesizeKeyEvent(true, 1, LOBYTE(zeroKey), 0, wch, ctrlState));
+            continue;
+        }
+        _storage.push_back(SynthesizeKeyEvent(true, 1, 0, 0, wch, 0));
+    }
+}
+
 TerminalInput& InputBuffer::GetTerminalInput()
 {
     return _termInput;

src/host/inputBuffer.hpp

@@ -58,6 +58,7 @@ public:
     size_t Prepend(const std::span<const INPUT_RECORD>& inEvents);
     size_t Write(const INPUT_RECORD& inEvent);
     size_t Write(const std::span<const INPUT_RECORD>& inEvents);
+    void WriteString(const std::wstring_view& text);
     void WriteFocusEvent(bool focused) noexcept;
     bool WriteMouseEvent(til::point position, unsigned int button, short keyState, short wheelDelta);
 
@@ -96,6 +97,7 @@ private:
     void _WriteBuffer(const std::span<const INPUT_RECORD>& inRecords, _Out_ size_t& eventsWritten, _Out_ bool& setWaitEvent);
     bool _CoalesceEvent(const INPUT_RECORD& inEvent) noexcept;
     void _HandleTerminalInputCallback(const Microsoft::Console::VirtualTerminal::TerminalInput::StringType& text);
+    void _writeString(const std::wstring_view& text);
 
 #ifdef UNIT_TESTING
     friend class InputBufferTests;

src/host/outputStream.cpp

@@ -33,24 +33,11 @@ ConhostInternalGetSet::ConhostInternalGetSet(_In_ IIoProvider& io) :
 // - <none>
 void ConhostInternalGetSet::ReturnResponse(const std::wstring_view response)
 {
-    InputEventQueue inEvents;
-
-    // generate a paired key down and key up event for every
-    // character to be sent into the console's input buffer
-    for (const auto& wch : response)
-    {
-        // This wasn't from a real keyboard, so we're leaving key/scan codes blank.
-        auto keyEvent = SynthesizeKeyEvent(true, 1, 0, 0, wch, 0);
-        inEvents.push_back(keyEvent);
-        keyEvent.Event.KeyEvent.bKeyDown = false;
-        inEvents.push_back(keyEvent);
-    }
-
     // TODO GH#4954 During the input refactor we may want to add a "priority" input list
     // to make sure that "response" input is spooled directly into the application.
     // We switched this to an append (vs. a prepend) to fix GH#1637, a bug where two CPR
     // could collide with each other.
-    _io.GetActiveInputBuffer()->Write(inEvents);
+    _io.GetActiveInputBuffer()->WriteString(response);
 }
 
 // Routine Description: