validate runtime objects (e.g. package.json, settings.json, etc) with zod or other "data validation" library

## Problem

For validating unknown input/data (`package.json`, `settings.json`, `globalState`, ...) at runtime we use either [ad-hoc procedural logic](https://github.com/aws/aws-toolkit-vscode/blob/5439f9527224d8d1c0b98cd9941ee55a0cefb9ae/src/shared/sam/debugger/awsSamDebugConfigurationValidator.ts#L33-L94) or typescript type generators: https://github.com/aws/aws-toolkit-vscode/blob/5439f9527224d8d1c0b98cd9941ee55a0cefb9ae/src/shared/settings.ts#L458-L482

## Solution

TypScript ecosystem now has rather mature libraries like [zod](https://www.youtube.com/watch?v=CughWjaoXZw) which achieve something similar to clojure's [spec](https://clojure.org/guides/spec): rich description of objects with runtime-checking (as opposed to typescript's compile-time-only checking).

- use zod(?) to replace [AwsSamDebugConfigurationValidator](https://github.com/aws/aws-toolkit-vscode/blob/8182aa558ed2b9a144ab9dff5b55b2abcedd4ef3/src/shared/sam/debugger/awsSamDebugConfigurationValidator.ts), [sharedCredentialsValidation.ts](https://github.com/aws/aws-toolkit-vscode/pull/3409)
- zod is an extra dependency, but itself has zero transitive dependencies.
- zod specs can also be used to _define_ TypeScript types, which avoids duplication for cases where you need both.
- via `z.infer()`

Start by reading src/shared/sam/debugger/awsSamDebugConfigurationValidator.ts and the generated type logic in src/shared/settings.ts. Review the referenced sharedCredentialsValidation.ts change and determine which runtime objects are in scope for a common validation approach. Done means the named validators are replaced or unified while preserving runtime checks and TypeScript type support.

Written by the indexing model from the issue text.