Fix space room reorder

[lhjt]

Description

• Prevent duplicate entries during same-space drag reorder by removing the dragged room before reinserting
• Ensure a single m.space.child update per room when reordering within a space
• This issue manifested itself as failing to update space room ordering when dragging a room upwards for the first time

Fixes #

Type of change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings