Feature: Add default name and auto-select text when creating new folder

[marlenhalvorsen]

Issue:
Closes #17845

Changes:

• Adds subtitle "Enter an item name" in create-item dialog
• Sets default name to "New folder" when creating folder
• Selects name by default to allow fast rename

Test steps:

1. Launch Files (debug build)
2. Create new folder via Ctrl+Shift+N
3. Check that:
   • The dialog shows subtitle "Enter an item name"
   • "New folder" is prefilled
   • Text is fully selected on open

[yaira2]

@marlenhalvorsen it looks like this is missing the Enter an item name subtitle. Can you adjust this?

[marlenhalvorsen]

Subtitle added. “Enter an item name” now appears correctly in the create-item dialog.

[yaira2]

Thanks! Should we apply this change for other file formats as well?

[marlenhalvorsen]

Thanks for the suggestion!

I've looked into the handling of itemType in GetFor_CreateItemDialog, and currently the dialog only receives two categories: "Folder" and "File". All file templates (e.g. .pptx, .xlsx, .txt) are mapped to "File" without any specific extension or template metadata.

Because of this, only the folder case can receive a unique default label at the moment. Differentiating per file type (e.g. "New .pptx", "New .xlsx") would require passing additional ShellNewEntry/extension information into the dialog.

[yaira2]

Thanks for checking. We can merge as is and can reconsider if we receive more feedback regarding other file formats.

[yaira2]

LGTM

[yaira2]

Alternatively, we can use "New document" for other file formats.