Query Planner Unable to Find Struct Fields with Capital Letters

### Describe the bug

If you create a table with a struct column where a field in the struct include a capital letter then the query planner will complain that it cannot find that field.

### To Reproduce

1. Create a JSON file named "test.json" with content:

{"thing": {"fooBar": "not going to find me"}}

2. Start the Datafusion cli
3. Execute "select thing.fooBar from 'test.json';"

Actual: The query will fail saying 'Error during planning: Field foobar not found in struct'.
Expected: The query executes returning 1 row with content "not going to find me"

Note: if you change the content of the file to:

{"thing": {"foobar": "not going to find me"}}

where the only change is "fooBar" to "foobar" then everything works.

### Expected behavior

Expected: The query executes returning 1 row with content "not going to find me"

Note: if you change the content of the file to:

{"thing": {"foobar": "not going to find me"}}

where the only change is "fooBar" to "foobar" then everything works.

### Additional context

Repros on 46.0.0 and 48.0.0

Start by reproducing the issue in the DataFusion CLI with the provided test.json and query. Trace the query-planner handling of struct field names to determine why fooBar becomes foobar. Done means the query returns the expected value for fooBar while the existing lowercase case continues to work.

Written by the indexing model from the issue text.