XML/JSON change for disabled blocks

[NeilFraser]

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Description

The XML save format is changing from

disabled="true"

to

disabled-reasons="MANUALLY_DISABLED"

Loading the former in v11 results in this console warning:

disabled was deprecated in v11 and will be deleted in v12.
Use disabled-reasons with the value "MANUALLY_DISABLED" instead.

It is utterly unprecedented to deprecate a core part of the XML parser. XML lives forever in external databases. This implies that v12 will no longer be able to load existing user code!

The offending code is here:
https://github.com/google/blockly/blob/rc/v11.0.0/core/xml.ts#L1024

Reproduction steps

1. Open the 'Logic' category in the playground. Since the 'null' block is disabled, a warning is printed.

Stack trace

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Screenshots

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Browsers

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[NeilFraser]

The same issue is true for JSON serialization.

Furthermore, the new XML/JSON serialization is not backwards compatible. In practice this is a lesser problem, but none-the-less, there's no reason to needlessly break V10 versions of Blockly getting V11 serialization.

[NeilFraser]

This was introduced by #7958. @johnnesky

[BeksOmega]

Good point, we shouldn't delete support for the old format, but we should migrate to the new one, because it fixes several bugs.

So the TODO here is to remove the deprecation warnings.

[NeilFraser]

Ok, I'll take it.

[johnnesky]

Yeah we can remove the deprecation warnings.

If you don't mind redundant data, we could also continue to serialize the old properties (when the disabled reason MANUALLY_DISABLED is present) for backwards compatibility.

[BeksOmega]

I think it's fine as long as we deserialize the old attributes. Serializing them is less important, and there are partners that really care about keeping save file sizes small since they're financially constrained (I.E. App Inventor will be grumpy with me).