Discover - count() over nullable boolean fields displays `null` value as false

### Environment

SaaS (https://sentry.io/)

### Steps to Reproduce

I believe I found an issue in how Discover handles `count()` of nullable boolean fields, and specifically how it handles null values - they seem to still be treated as false, but then get translated to the wrong query when you try to look at the group with that result.

Do a count() over the `error.main-thread` field:


### Expected Result

The count() should give back a single line with result `null` for all the events which have a null value for the field (which are all of them in the case of my query, thats why there is only one line).

I should then be able to click "View Group" (the button on the side of the row) and reach a search for `!has:error.main_thread` because this is a boolean field.

### Actual Result

it looks like they are all with false value:


but in fact if you check you will see these all actually have "null" value. When you click the on "view group", you get an error saying boolean must be 1 or 0, since its querying for `error.main-thread is ""`:


This happens because the actual value it found on all the events is a null value, and boolean fields can't query for null, they have to do `!has:error.main-thread`.

The way I see it there are two issues here - it should display "null" as the value, and not false, and when viewing group the query should be different.

### Product Area

Discover

### Link

sentry

### DSN

_No response_

### Version

_No response_

Start by reproducing the Discover count() query on the nullable error.main-thread field and inspect the Discover aggregation and View Group query entry points. Done means nullable results display as null, and View Group generates !has:error.main-thread instead of a boolean equality query; add or update coverage for both behaviors.

Written by the indexing model from the issue text.