Automatically convert paths dropped on WSL instances (#11625)

Drag and drop does not work for WSL because paths are pasted as windows
paths having incorrect path separator and path root.  This PR adds code
to correct the path in TerminalControl before pasting to WSL terminals.

One problem with this approach is that it assumes the default WSL
automount root of "/mnt". It would be possible to add a setting like
"WslDragAndDropMountRoot"... but I decided it if someone wants to change
automount location it would be simple enough just to create the "/mnt"
symlink in WSL.

## Validation
Couldn't find an obvious place to add a test.  Manually tested
cut-n-paste from following paths:
- "c:\"
- "c:\subdir"
- "c:\subdir\subdir"
- "\\wsl.localhost\<distro>"
- \\wsl.localhost\<distro>\subdir"

Closes #331

.github/actions/spelling/allow/allow.txt

@@ -41,6 +41,7 @@ Lmid
 Lorigin
 maxed
 mkmk
+mnt
 mru
 noreply
 nje

src/cascadia/TerminalControl/IControlSettings.idl

@@ -27,6 +27,7 @@ namespace Microsoft.Terminal.Control
     interface IControlSettings requires Microsoft.Terminal.Core.ICoreSettings, Microsoft.Terminal.Control.IControlAppearance
     {
         String ProfileName;
+        String ProfileSource;
 
         Boolean UseAcrylic;
         ScrollbarState ScrollState;

src/cascadia/TerminalControl/TermControl.cpp

@@ -2271,6 +2271,42 @@ namespace winrt::Microsoft::Terminal::Control::implementation
                     }
 
                     std::wstring fullPath{ item.Path() };
+
+                    // Fix path for WSL
+                    if (_settings.ProfileSource() == L"Windows.Terminal.Wsl")
+                    {
+                        std::replace(fullPath.begin(), fullPath.end(), L'\\', L'/');
+
+                        if (fullPath.size() >= 2 && fullPath.at(1) == L':')
+                        {
+                            // C:/foo/bar -> Cc/foo/bar
+                            fullPath.at(1) = til::tolower_ascii(fullPath.at(0));
+                            // Cc/foo/bar -> /mnt/c/foo/bar
+                            fullPath.replace(0, 1, L"/mnt/");
+                        }
+                        else
+                        {
+                            static constexpr std::wstring_view wslPathPrefixes[] = { L"//wsl.localhost/", L"//wsl$/" };
+                            for (auto prefix : wslPathPrefixes)
+                            {
+                                if (til::starts_with(fullPath, prefix))
+                                {
+                                    if (const auto idx = fullPath.find(L'/', prefix.size()); idx != std::wstring::npos)
+                                    {
+                                        // //wsl.localhost/Ubuntu-18.04/foo/bar -> /foo/bar
+                                        fullPath.erase(0, idx);
+                                    }
+                                    else
+                                    {
+                                        // //wsl.localhost/Ubuntu-18.04 -> /
+                                        fullPath = L"/";
+                                    }
+                                    break;
+                                }
+                            }
+                        }
+                    }
+
                     const auto containsSpaces = std::find(fullPath.begin(),
                                                           fullPath.end(),
                                                           L' ') != fullPath.end();
@@ -2283,6 +2319,7 @@ namespace winrt::Microsoft::Terminal::Control::implementation
 
                     allPaths += fullPath;
                 }
+
                 _core.PasteText(winrt::hstring{ allPaths });
             }
         }

src/cascadia/TerminalSettingsModel/TerminalSettings.cpp

@@ -275,6 +275,7 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
 
         // Fill in the remaining properties from the profile
         _ProfileName = profile.Name();
+        _ProfileSource = profile.Source();
         _UseAcrylic = profile.UseAcrylic();
 
         _FontFace = profile.FontInfo().FontFace();

src/cascadia/TerminalSettingsModel/TerminalSettings.h

@@ -119,6 +119,8 @@ namespace winrt::Microsoft::Terminal::Settings::Model::implementation
         // ------------------------ End of Core Settings -----------------------
 
         INHERITABLE_SETTING(Model::TerminalSettings, hstring, ProfileName);
+        INHERITABLE_SETTING(Model::TerminalSettings, hstring, ProfileSource);
+
         INHERITABLE_SETTING(Model::TerminalSettings, bool, UseAcrylic, false);
         INHERITABLE_SETTING(Model::TerminalSettings, double, Opacity, UseAcrylic() ? 0.5 : 1.0);
         INHERITABLE_SETTING(Model::TerminalSettings, hstring, Padding, DEFAULT_PADDING);

src/cascadia/UnitTests_Control/MockControlSettings.h

@@ -51,6 +51,7 @@ namespace ControlUnitTests
         // ------------------------ End of Core Settings -----------------------
 
         WINRT_PROPERTY(winrt::hstring, ProfileName);
+        WINRT_PROPERTY(winrt::hstring, ProfileSource);
         WINRT_PROPERTY(bool, UseAcrylic, false);
         WINRT_PROPERTY(double, Opacity, .5);
         WINRT_PROPERTY(winrt::hstring, Padding, DEFAULT_PADDING);