class ReplaceComponentDecl

Replaces the component decl for the given component. `name` must

refer to a component that is one of the following:

- A component with a local implementation

- A legacy component

- A component added with a fragment-only URL (typically, components

bundled in the same package as the realm builder client, sharing the

same `/pkg` directory, for example, `#meta/other-component.cm`; see

https://fuchsia.dev/fuchsia-src/reference/components/url#relative-fragment-only)

- An automatically generated realm (ex: the root)

Errors:

- `NO_SUCH_CHILD`: This realm does not contain a child with the given

name.

- `CHILD_ALREADY_EXISTS`: The component whose decl is being replaced has

had a child added to it through realm builder with the same name as an

element in `component_decl.children`.

- `CHILD_DECL_NOT_VISIBLE`: The component decl cannot be manipulated for

the referenced child, because the child was added to the realm using

an absolute (not relative) and modern (not legacy) URL.

- `INVALID_COMPONENT_DECL`: `component_decl` failed validation.

- `BUILD_ALREADY_CALLED`: The `Builder.Build` function has been called

for this realm, and thus this `Realm` channel can no longer be used.