Allow As*Map* and As*Array* functions to perform inner conversions

[iwahbe]

Hello!

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Issue details

Calling any of our As*Map* or As*Array* methods performs a direct cast on the awaited value, with no attempt to ensure the conversion is valid. This is particularly painful in go, since it is not valid to case a value x from []interface{} to []string, even if every value in x is itself a string. We should modify this behavior to be more tolerant, allowing casts where each inner type is a valid cast.

This change can be most easily expressed by showing the new code:

old code:

func (a AnyOutput) AsStringMapOutput() StringMapOutput {
	return a.ApplyT(func(i interface{}) map[string]string {
		return i.(map[string]string)
	}).(StringMapOutput)
}

new code:

func (a AnyOutput) AsStringMapOutput() StringMapOutput {
	return a.ApplyT(func(i interface{}) map[string]string {
		v, ok := i.(map[string]string)
                if ok { return v }
		v := map[string]string{}
		vAny, ok := i.(map[string]interface{})
                if !ok { 
			panic(fmt.Sprintf("expected map[string]string or map[string]interface{}, found %T", i))
		}
		for k, val := range vAny {
			sVal, ok := val.(string)
			if !ok {
				panic(fmt.Sprintf("Key %s has an invalid value of type %T, must be a string", val)
			}
			v[k] = sVal
		}
		return v
	}).(StringMapOutput)
}

Inspired by #11347.

Affected area/feature

[iwahbe]

Partially implemented by #10991.