[codegen/node] Add config to enable type splitting

[RobbieMcKinstry]

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Issue details

Splitting NodeJS types files into smaller units created two P0 issues.

• Node.js split types generated code is not usable #11531
• Latest pulumi codegen version makes nodejs unreleasable pulumi-azure-native#2108

To guard against this, we would like to add a toggle to enable this feature in the SDK schema. This feature is to add the old behavior back in, but guard against it with a schema toggle.

This will allow us to continue to iterate on the existing work without disrupting providers. It will also allow providers to opt into this feature in the future at their leisure.

The toggle will default to "off".

Affected area/feature

codegen/nodejs