Add setting for customizable delimiter for file drag-and-drop

[Vallabh-1504]

Summary of the Pull Request

This PR introduces a new profile setting, dragDropDelimiter, which allows users to configure the string separator used when dragging and dropping multiple files into the terminal. The default behavior remains a single space (" ") for backward compatibility.

References and Relevant Issues

• Closes Configurable delimiter when drag-and-drop multiple files #19565

Detailed Description of the Pull Request / Additional comments

Implementation Details:

• Settings: Added DragDropDelimiter to MTSMSettings.h and Profile.idl.
• Control: Wired the setting through ControlProperties.h so the terminal logic can see it.
• Logic: Updated TermControl::OnDrop to use the new delimiter when joining paths.
• UI: Added the text box in the Advanced Settings page and updated the ViewModel.

Demo

demo1.mp4

Validation Steps Performed

• Manual Verification:
  • Verified default behavior (space separator) works as before.
  • Configured dragDropDelimiter to ", ", ";", and custom strings in settings.json and from settings UI.
  • Confirmed dropped files are joined correctly.
• Build: Validated that the solution builds cleanly.

Notes for Reviewers

1. Delimiter Length: Currently, there is no limit on the maximum length of the delimiter string. Let me know if this should be changed.
2. Localization: I changed only Resources/en-US file.
3. ViewModel: In ProfileViewModel.cpp, I added the else if block for the new setting, but left it empty because no other UI logic currently depends on it.

PR Checklist

• Closes Configurable delimiter when drag-and-drop multiple files #19565
• Tests added/passed
• Documentation updated
• Schema updated (if necessary)

[Copilot]

Pull request overview

This PR adds a new profile setting dragDropDelimiter that allows users to customize the delimiter used when dragging and dropping multiple files into the terminal. The default delimiter remains a single space for backward compatibility, but users can now configure it to use comma-space, semicolon, or any custom string to match their shell's syntax requirements (e.g., PowerShell's comma-separated paths).

Changes:

• Added dragDropDelimiter profile setting to the settings model, control properties, and UI with a default value of " " (single space)
• Updated drag-and-drop logic in TermControl to use the configurable delimiter instead of hardcoded space
• Added settings UI in the Advanced tab with localized strings for the delimiter configuration

Reviewed changes

Copilot reviewed 12 out of 12 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/cascadia/TerminalSettingsModel/MTSMSettings.h	Added dragDropDelimiter to profile settings macro with default value L" "
src/cascadia/TerminalSettingsModel/Profile.idl	Added DragDropDelimiter as inheritable profile setting
src/cascadia/inc/ControlProperties.h	Added DragDropDelimiter to control properties macro
src/cascadia/TerminalControl/IControlSettings.idl	Exposed DragDropDelimiter getter in control settings interface
src/cascadia/TerminalControl/TermControl.cpp	Updated file drop logic to use configurable delimiter instead of hardcoded space
src/cascadia/TerminalSettingsEditor/ProfileViewModel.idl	Added DragDropDelimiter to observable projected profile settings
src/cascadia/TerminalSettingsEditor/ProfileViewModel.h	Added macro entry for DragDropDelimiter observable setting
src/cascadia/TerminalSettingsEditor/ProfileViewModel.cpp	Added empty property change handler (unnecessary code added)
src/cascadia/TerminalSettingsEditor/Profiles_Advanced.xaml	Added TextBox UI control for drag/drop delimiter configuration
src/cascadia/TerminalSettingsAppAdapterLib/TerminalSettings.cpp	Initialized DragDropDelimiter from profile settings
src/cascadia/TerminalSettingsEditor/Resources/en-US/Resources.resw	Added localized strings with critical XML syntax error (missing closing tag)
doc/cascadia/profiles.schema.json	Added dragDropDelimiter schema entry with type string and default value

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[Copilot]

The new dragDropDelimiter setting lacks test coverage. The repository has comprehensive serialization tests in src/cascadia/UnitTests_SettingsModel/SerializationTests.cpp for profile settings. Consider adding a test case that verifies the setting can be properly serialized and deserialized, similar to how other profile settings are tested in the Profile() test method.

[Copilot]

Missing x:Name attribute on the SettingContainer. All other SettingContainer elements in this file have x:Name attributes for consistency (e.g., "ShowMarks", "RainbowSuggestions", "PathTranslationStyle"). Add x:Name="DragDropDelimiter" to line 276.

Suggested change

	<local:SettingContainer x:Uid="Profile_DragDropDelimiter"
	<local:SettingContainer x:Name="DragDropDelimiter"
	x:Uid="Profile_DragDropDelimiter"

[Copilot]

Missing closing tag for the data element. The opening tag on line 2728 is not properly closed before the next data element begins on line 2731. Add a closing </data> tag after line 2730.

Suggested change

	<comment>A description for what the "drag drop delimiter" setting does.</comment>
	<comment>A description for what the "drag drop delimiter" setting does.</comment>
	</data>

[Copilot]

The empty else-if block is unnecessary. Settings that don't have derived properties don't need handlers in the PropertyChanged event. Consider removing this entire else-if block (lines 109-113) to reduce clutter. Many other simple settings like AllowVtClipboardWrite, RainbowSuggestions, etc. don't have handlers here.

Suggested change

	else if (viewModelProperty == L"DragDropDelimiter")
	{
	// No specific computed property depends on this
	// we can add _NotifyChanges(), if required
	}