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## Description

When we generate a JSON schema via `schemars`, we end up with duplicate
types in the schema, which get names like `ValueExpression2`, `Role2`,
and so on. This isn't ideal, and seems to arise for two reasons:

1. The type is polymorphic, and is monomorphised in two ways, and thus
the types can't be unified.
2. The type is monomorphic, but is used inside and outside of its home
module.

The first problem was fixed previously by splitting polymorphic types,
but the second has proven to be a bit more work. This PR finally solves
the problem by introducing a new library, `jsonschema-tidying`:

* First, we search the definitions within the JSON schema for any whose
names end in a number, such as `ValueExpression2` or `MetadataV2`.
* Then, we look for types whose names match everything up to the final
numeric digits, and discard any types for whom we can't find a match (so
we keep `ValueExpression2` because `ValueExpression` exists, but discard
`MetadataV2` because `MetadataV` does not).
* Next, we remove the duplicate definition from the definitions map,
potentially breaking links in both the schema _and_ the rest of the
definitions map.
* Finally, we traverse the entirety of the tree looking for any
references to the duplicate entry, and replace them with references to
the original entry.

This PR has no direct user-facing change, however it _will_ have an
effect on the docs generation code, which will hopefully result in
tidier documentation.

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### Product

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- [ ] community-edition
- [ ] cloud
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V3_GIT_ORIGIN_REV_ID: fe73acf7d9df0b9867852e673e53cb086e3725d3