Fix numerous blend space issues

[Ryan-000]

Resolves #118945 #118982

[TokageItLab]

Since it appears to contain numerous changes beyond the fixes for the reported issues, you need to split it up; Since now is the beta phase, only fixes for avoiding crash should be applied here. You can create a separate PR or modify this PR that addresses only the BlendSpace1D/2D "Editor" crash fix (so I assume we should change only BlendSpace1D/2DEditor class not BlendSpace1D/2D class). See also #118970 to avoid conflict/duplication with that.

If you really need to make changes, you must provide a detailed explanation of the cause and the solution in the description. This PR appears to make overly fundamental changes to address the issue.

[vaner-org]

No conflicts with #118970, that one only targets editors, this one mostly targets resources.

[fire]

The changes are too scattered, I can't tell the logical reason for the changes linked to a bug report.

[Ryan-000]

Bugsquad edited:

Superseded by

• Fix undo crash when animation editor is not active #119061
• Do not restore triangles when the blendspace has auto_triangles enabled #119062
• Animation: Only erase properties for a specific node #119063
• Fix validate_node not running after triangles are modified. #119064
• Correct ERR_FAIL_INDEX_V in AnimationNodeBlendSpace #119065
• Validate name in add_blend_point and forbid duplicates #119066
• Regenerate auto triangles when a blend point is removed #119067
• Reset closest parameter when child is removed from BlendSpace #119068
• Fix BlendSpace point insertion shift at a specific index #119069
• Blend space editor: Use correct name in events, and clean all states #119070