Support creating new scene autoloads from menu

[Zshandi]

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Fixes #107131

Update the test for the file picker to make it clear it supports scripts and scenes Update the "Add" button to open a drop-down instead of just adding a script

• The drop-down has options for both "Script" and "Scene"
• "Scene" opens the usual scene creation popup, but with one change
• Create scene window updated to allow calling into it from the autoloads section Create scene window allows editing the directory via a new "Scene Path" field
• Only allows entering a directory, not the full file path
• This is a config option, so the regular create scene window (accessed from the File Browser) still functions exactly as it did