PR: Initial file dialog definition to select a remote directory (Remote Client)

[dalthviz]

Description of Changes

• Added a test
• Wrote at least one-line docstrings (for any new functions)
• Included a screenshot or animation (if affecting the UI, see Licecap)

• Add RemoteFileDialog class definition with a static method to retrieve a directory path
• Add a kwarg to the RemoteExplorer to show only directories

Issue(s) Resolved

Part of #12828

Affirmation

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and understand I am releasing the same under Spyder's MIT (Expat) license.

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[ccordoba12]

@dalthviz, quick feedback according to the screenshot you posted:

• Headers (i.e. Name and Size) shouldn't be visible.

• The tree lines to the left shouldn't be visible either.

• Folder and file icons should be a bit bigger (perhaps 22px) to display them differently from the regular remote file explorer

• Ideally they should be arranged in a grid (but that's not a must), like this (from the KDE file dialog)