CQ. Create TypeParameterElementImpl instances in owning elements.

Create `TypeParameterElementImpl` instances when their owning elements
are constructed, instead of materializing them later in builders,
fragment linkers, and bundle reading. This makes ownership explicit in
the element model.

Update synthetic executable construction in inheritance handling to
build fresh type parameter and formal parameter elements. Top-merge and
covariance inheritance were previously able to reuse fragments from
other executables, which could attach fragments to the wrong element and
produce invalid synthetic members for generic signatures.

For type aliases, serialize the first fragment directly instead of a
fragment list. This matches how type alias elements are constructed and
avoids a separate read-time step that recreated type parameter elements.

Bump the data version for the format change.

Change-Id: If4f203f65fb11bcd0ffd1dcc0e47956b9fb2597b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/496780
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>