[C++] Enable Substrait ReadRel Projection in Acero

### Describe the enhancement requested

At the moment, Acero-Substrait integration doesn't support projection in the `ReadRel`. To enable this of the main contibutions is to consume `MaskExpressions` in Acero. A sample Substrait plan is shown below. At the moment this plan cannot be consumed using Acero.

```json
{
"extensions": [
{
"extensionFunction": {
"functionAnchor": 1,
"name": "equal"
}
}
],
"relations": [
{
"root": {
"input": {
"project": {
"input": {
"project": {
"input": {
"join": {
"left": {
"read": {
"baseSchema": {
"names": [
"o_orderkey",
"o_custkey",
"o_orderstatus",
"o_totalprice",
"o_orderdate",
"o_orderpriority",
"o_clerk",
"o_shippriority",
"o_comment"
],
"struct": {
"types": [
{
"i32": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i32": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 1,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"decimal": {
"scale": 2,
"precision": 15,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"date": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 15,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 15,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i32": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 78,
"nullability": "NULLABILITY_NULLABLE"
}
}
],
"nullability": "NULLABILITY_REQUIRED"
}
},
"projection": {
"select": {
"structItems": [
{
"field": 1
}
]
},
"maintainSingularStruct": true
},
"namedTable": {
"names": [
"orders"
]
}
}
},
"right": {
"read": {
"baseSchema": {
"names": [
"c_custkey",
"c_name",
"c_address",
"c_nationkey",
"c_phone",
"c_acctbal",
"c_mktsegment",
"c_comment"
],
"struct": {
"types": [
{
"i32": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 18,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 40,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"i32": {
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 15,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"decimal": {
"scale": 2,
"precision": 15,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 10,
"nullability": "NULLABILITY_NULLABLE"
}
},
{
"varchar": {
"length": 116,
"nullability": "NULLABILITY_NULLABLE"
}
}
],
"nullability": "NULLABILITY_REQUIRED"
}
},
"projection": {
"select": {
"structItems": [
{}
]
},
"maintainSingularStruct": true
},
"namedTable": {
"names": [
"customer"
]
}
}
},
"expression": {
"scalarFunction": {
"functionReference": 1,
"outputType": {
"bool": {
"nullability": "NULLABILITY_NULLABLE"
}
},
"arguments": [
{
"value": {
"selection": {
"directReference": {
"structField": {}
},
"rootReference": {}
}
}
},
{
"value": {
"selection": {
"directReference": {
"structField": {
"field": 1
}
},
"rootReference": {}
}
}
}
]
}
},
"type": "JOIN_TYPE_INNER"
}
},
"expressions": [
{
"selection": {
"directReference": {
"structField": {}
},
"rootReference": {}
}
},
{
"selection": {
"directReference": {
"structField": {
"field": 1
}
},
"rootReference": {}
}
}
]
}
},
"expressions": [
{
"selection": {
"directReference": {
"structField": {}
},
"rootReference": {}
}
}
]
}
},
"names": [
"o_custkey"
]
}
}
]
}
```

### Component(s)

C++

Start with the Acero-Substrait integration's current ReadRel handling and the sample Substrait plan in this issue, focusing on the projection and its MaskExpressions. Done means Acero can consume the shown plan with projected ReadRel inputs, including the nested projections described in the request.

Written by the indexing model from the issue text.