(stepfunctions-tasks): DynamoDB attribute map synth output

### Describe the bug

sfntask.DynamoAttributeValue.mapFromJsonPath --> $.$.M
>
const addNewDocVersion2 = new sfntask.DynamoPutItem(this, 'addNewDocVersion2', {
table: props.formtable,
item: {
Id: sfntask.DynamoAttributeValue.fromString(sfn.JsonPath.stringAt('$.Item.Id.S')),
sk: sfntask.DynamoAttributeValue.fromString(sfn.JsonPath.format('v{}',sfn.JsonPath.stringAt('$.latest_version.latest_version.N'))),
BusinessRule: sfntask.DynamoAttributeValue.mapFromJsonPath(sfn.JsonPath.stringAt('$.Item.BusinessRule.M')),
Status: sfntask.DynamoAttributeValue.fromString('BusinessRuleProcessed'),
Updated: sfntask.DynamoAttributeValue.fromNumber(businessRuleTS),
Table: sfntask.DynamoAttributeValue.listFromJsonPath(sfn.JsonPath.stringAt('$.Item.Table.L')),
KeyValue: sfntask.DynamoAttributeValue.mapFromJsonPath(sfn.JsonPath.stringAt('$.Item.KeyValue.M')),
},
resultPath: JsonPath.DISCARD
})

It turns into:

>

"Parameters": {
"Item": {
"Id": {
"S.$": "$.Item.Id.S"
},
"sk": {
"S.$": "States.Format('v{}', $.latest_version.latest_version.N)"
},
"BusinessRule": {
"M.$.$": "$.Item.BusinessRule.M"
},
"Status": {
"S": "BusinessRuleProcessed"
},
"Updated": {
"N": "1657831854044"
},
"Table": {
"L.$": "$.Item.Table.L"
},
"KeyValue": {
"M.$.$": "$.Item.KeyValue.M"
}
},

### Expected Behavior

sfntask.DynamoAttributeValue.mapFromJsonPath Should be $.M

### Current Behavior

sfntask.DynamoAttributeValue.mapFromJsonPath should not be $.$.M

### Reproduction Steps

const addNewDocVersion2 = new sfntask.DynamoPutItem(this, 'addNewDocVersion2', {
table: props.formtable,
item: {
Id: sfntask.DynamoAttributeValue.fromString(sfn.JsonPath.stringAt('$.Item.Id.S')),
sk: sfntask.DynamoAttributeValue.fromString(sfn.JsonPath.format('v{}',sfn.JsonPath.stringAt('$.latest_version.latest_version.N'))),
BusinessRule: sfntask.DynamoAttributeValue.mapFromJsonPath(sfn.JsonPath.stringAt('$.Item.BusinessRule.M')),
Status: sfntask.DynamoAttributeValue.fromString('BusinessRuleProcessed'),
Updated: sfntask.DynamoAttributeValue.fromNumber(businessRuleTS),
Table: sfntask.DynamoAttributeValue.listFromJsonPath(sfn.JsonPath.stringAt('$.Item.Table.L')),
KeyValue: sfntask.DynamoAttributeValue.mapFromJsonPath(sfn.JsonPath.stringAt('$.Item.KeyValue.M')),
},
resultPath: JsonPath.DISCARD
})

### Possible Solution

_No response_

### Additional Information/Context

_No response_

### CDK CLI Version

2.31.2

### Framework Version

_No response_

### Node.js Version

v14.17.6

### OS

Mac OS

### Language

Typescript

### Language Version

TypeScript 4.7.4

### Other information

_No response_

Start at DynamoAttributeValue.mapFromJsonPath and reproduce the issue with the shown DynamoPutItem configuration. Compare the synthesized Step Functions Parameters output for BusinessRule and KeyValue; done means mapFromJsonPath emits M.$ with the JSONPath rather than M.$.$.

Written by the indexing model from the issue text.