[BUG] Boolean fields aren't applied as filters in WHERE clauses

[Swiddis]

What is the bug?
Building on #3266, it turns out that variables as boolean clauses aren't applied correctly at all.

How can one reproduce the bug?

PUT test_index

POST _bulk
{ "create": { "_index": "test_index" } }
{ "x": 0, "y": false }
{ "create": { "_index": "test_index" } }
{ "x": 1, "y": true }
{ "create": { "_index": "test_index" } }
{ "x": 2, "y": null }

POST _plugins/_sql
{
  "query": "SELECT x FROM test_index WHERE y"
}
{
  "schema": [
    {
      "name": "x",
      "type": "long"
    }
  ],
  "datarows": [
    [0], [1], [2]
  ],
  "total": 3,
  "size": 3,
  "status": 200
}

What is the expected behavior?

{
  "schema": [
    {
      "name": "x",
      "type": "long"
    }
  ],
  "datarows": [
    [1]
  ],
  "total": 1,
  "size": 1,
  "status": 200
}

What is your host/environment?

• Commit 1284c12

Do you have any screenshots?
N/A

Do you have any additional context?
Found by dynamic-testing via NoREC. Original failure:

Falsified after 0 passed tests.
> Labels of failing property: 
39 != 15
Optimizing:     SELECT j FROM test_34761613 WHERE z
Non-Optimizing: SELECT z FROM test_34761613 
> ARG_0: SELECT j, k FROM test_34761613 WHERE z

[LantaoJin]

After #3849 merged, the issue only could happen in v2. In v3 (enabling calcite)

POST /_plugins/_ppl
{
  "query": "source=test_index | WHERE y"
}

returns

{
  "schema": [
    {
      "name": "x",
      "type": "bigint"
    },
    {
      "name": "y",
      "type": "boolean"
    }
  ],
  "datarows": [
    [
      1,
      true
    ]
  ],
  "total": 1,
  "size": 1
}