Issue 64687. Resolve default values and constant initializers of all fragments.

The default value of every formal parameter fragment, and the constant
initializer of every variable fragment, is written into the bundle,
including fragments of augmentations. Previously at most one fragment
per element was resolved (the first, or for typed constants the last one
with an initializer), so the others were written unresolved, e.g. with
`staticType: null`.

`DefaultValueResolver` now resolves the formal parameters of all
fragments of each executable, and also visits getters and setters, whose
formal parameters can exist in recovered code.
`ConstantInitializersResolver` now resolves the initializers of all
fragments, skipping only the first fragment's initializer when
`TopLevelInference` already resolved it to infer the type.

The context of a variable initializer during linking is now computed in
one place, `AstResolver.resolveVariableInitializerForLinking`, used by
both type inference and `ConstantInitializersResolver`: the enclosing
interface, whether `this` is accessible (late instance fields), and the
in-scope primary constructor parameters (non-late instance fields).
Previously `ConstantInitializersResolver` passed no enclosing class and
never made `this` accessible, so `this` and implicit `this` references
in typed initializers resolved to `InvalidType`, unlike the same
initializers without a type annotation.

As a result, typed field initializers that reference instance members
now get the same constant evaluation diagnostics as untyped ones,
`invalidConstant` and `constInitializedWithNonConstantValue`, in
addition to `implicitThisReferenceInInitializer`.

Bug: https://github.com/dart-lang/sdk/issues/64687
Change-Id: I291e98bc5ed0f6d63ebd52fc8f1fcdb7ce05d5ad
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/568162
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>