Ensure `type` decls are types

[mtzguido]

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This fixes #2933 by adding a Type ascription whenever none is present.

This does lead to some regressions, since if there was no ascription / expected type we would take one from the corresponding val, if any, but now we do not. This means in some places we must manually annotate some things, duplicating information from the val.

Here's the full F* regressions (some of them are legit problems now caught) https://github.com/FStarLang/FStar/commit/d5e7844d8aaeff18c814bb0e3ab0f4044e5939b2