[_fe_analyzer_shared] Renames to prepare for analyzer refactoring.

The following shared getters are renamed so that their names are
distinct from the corresponding getters in the analyzer:

- `SharedFunctionTypeStructure.positionalParameterTypes` is renamed to
  `positionalParameterTypesShared` to be distinct from the analyzer's
  public getter `FunctionType.positionalParameterTypes`.*

- `SharedFunctionTypeStructure.returnType` is renamed to
  `returnTypeShared` to be distinct from the analyzer's public getter
  `FunctionType.returnType`.

- `SharedNamedFunctionParameterStructure.type` is renamed to
  `typeShared` to be distinct from the analyzer's public getter
  `FormalParameterElement.type`.

- `SharedNamedTypeStructure.type` is renamed to `typeShared` to be
  distinct from the analyzer's public getter
  `RecordTypeNamedField.type`.

- `SharedRecordTypeStructure.positionalTypes` is renamed to
  `positionalTypesShared` to be distinct from the analyzer's public
  getter `RecordType.positionalTypes`.*

- `SharedRecordTypeStructure.sortedNamedTypes` is renamed to
  `sortedNamedTypesShared` to be distinct from the analyzer's public
  getter `RecordType.sortedNamedTypes`.

- `SharedTypeParameterStructure.bound` is renamed to `boundShared` to
  be distinct from the analyzer's public getter
  `TypeParameterElement2.bound`.

*Note that `FunctionType.positionalParameterTypes`,
 `RecordType.positionalTypes`, and `RecordType.sortedNamedTypes` were
 unintentionally exposed as part of the analyzer's public API. In a
 previous CL I marked them as deprecated.

These renames pave the way for changing the analyzer's `DartType`
class so that it implements `SharedTypeStructure<TypeImpl>` rather
than `SharedTypeStructure<DartType>` (without the renames, the public
getters mentioned above would all have to be changed to have type
`TypeImpl`, and that in turn would expose `TypeImpl` through the
analyzer public API, which we don't want to do).

Once `DartType` implements `SharedTypeStructure<TypeImpl>`, that will
allow all the other uses of `SharedTypeStructure<DartType>` in the
analyzer to be gradually migrated to
`SharedTypeStructure<TypeImpl>`. Once that is done, `DartType` can be
changed so that it no longer implements
`SharedTypeStructure<TypeImpl>` at all (`TypeImpl` will implement
`SharedTypeStructure<TypeImpl> instead). This will free us up to make
future changes to the `SharedTypeStructure` base class without
inadvertently exposing those changes through the analyzer public API.

This is part of a larger arc of work to change the analyzer's use of
the shared code so that the type parameters it supplies are not part
of the analyzer public API. See
https://github.com/dart-lang/sdk/issues/59763.

Change-Id: I0686fdeae304f8948484516f0249841b79e7da6c
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/403625
Reviewed-by: Chloe Stefantsova <cstefantsova@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>