DynamoDB KeyExpression are not evaluated the right way

[Kruspe]

When querying a table with a composite key like PK and SK depending on the brackets set inside the KeyConditions some queries fail.

Steps to reproduce:

1. Parsing the following key condition does not work at all

aws dynamodb query --table-name <TABLE_NAME> --endpoint-url <MOTO_ENDPOINT> --key-condition-expression "(#0 = :0) AND (BEGINS_WITH(#1, :1))" --expression-attribute-values '{":0": {"S": "TEST"}, ":1": {"S": "ABC"}}' --expression-attribute-names '{"#0": "PK", "#1": "SK"}'

This produces the following error with moto although it is a valid query:
An error occurred (ValidationException) when calling the Query operation: Query condition missed key schema element: SK

2. Given a table with a few entries like:

PK	SK
TEST	id#aa
TEST	id#ab
TEST	id#ad

aws dynamodb query --table-name <TABLE_NAME> --endpoint-url <MOTO_ENDPOINT> --key-condition-expression "(#0 = :0) AND (#1 BETWEEN :1 AND :2)" --expression-attribute-values '{":0": {"S": "TEST"}, ":1": {"S": "AB"}, ":2": {"S": "AB"}}' --expression-attribute-names '{"#0": "PK", "#1": "SK"}'

While this query should only return 1 item (the second item) it returns all three items from the table above.