Fix webview providerId not being restored on reload

[mjbvz]

Fixes #156491

[lramos15]

These additions seem like a good use case for Untyped Editor inputs. These untyped editor inputs can also be thought of as editor input DTOs which are used for the resolver service to contain the minimum set of information needed to resolve an editor. Not sure if we can use that here, it's also very similar to what we have as the editor representation in the tabs api. The untyped inputs can be found here

vscode/src/vs/workbench/common/editor.ts

Line 744 in bcba696

export type IUntypedEditorInput = IResourceEditorInput | ITextResourceEditorInput | IUntitledTextResourceEditorInput | IResourceDiffEditorInput | IResourceSideBySideEditorInput | IResourceMergeEditorInput;

(will probably soon be renamed to unresolved)