Fix WPF Pane implementation

[Wurschdhaud]

Description

correct infinite recursion in WPFPanel static methods; add dockable pane API coverage and panel registry

Bug fixes

WPFPanel.hide_element, show_element, toggle_element, disable_element, and enable_element were all calling themselves recursively (referencing WPFPanel instead of WPFWindow). These would blow the call stack immediately on first use. All five now correctly delegate to their WPFWindow counterparts.
is_registered_dockable_panel was calling UI.DockablePane.PaneExists corrected to PaneIsRegistered, consistent with how toggle_dockable_panel already called it.
panel_title was silently expected by register_dockable_panel but never validated in __init__ or declared as a class attribute. Added declaration and a guard matching the existing pattern for panel_id and panel_source.

New features

SetupDockablePane now populates the previously TODO'd fields on DockablePaneProviderData: InitialState, EditorInteraction, and ContextualHelp. These are driven by optional class attributes (initial_state, editor_interaction, contextual_help) on WPFPanel, so existing panels require no changes.
A module-level DOCKABLE_PANEL_REGISTRY dict now stores the live panel instance at registration time. get_dockable_panel(panel_type_or_id) exposes it, allowing any script to retrieve the live instance without re-registering — which was previously impossible without storing the return value of register_dockable_panel in a shared location manually.

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Checklist

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• Code follows the PEP 8 style guide.
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  pipenv run black {source_file_or_directory}

• Changes are tested and verified to work as expected.

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Pull request overview

Fixes pyrevit.forms dockable panel/WPF panel behavior by correcting broken WPFPanel element helper methods and improving dockable pane registration/configuration, including a registry for retrieving live panel instances.

Changes:

• Fix infinite recursion in WPFPanel static element helper methods by delegating to WPFWindow.
• Expand dockable pane provider setup to populate DockablePaneProviderData fields from optional WPFPanel class attributes.
• Add a module-level dockable panel registry plus get_dockable_panel() to retrieve the live panel instance after registration.

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📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1126-wip

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📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1139-wip

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📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1233-wip

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📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1244-wip

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📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1357-wip

[github-actions]

📦 New work-in-progress (wip) builds are available for 6.1.0.26061+1403-wip