Support query-time JSON parsing + nested field access + array expansion for Logs (KQL-like)

### Problem Statement

**Summary:**

Customers want to query semi-structured logs (JSON blobs / nested fields / arrays) without pre-tagging every field at ingestion time (schema-on-read like KQL). Today Sentry Logs are schema-on-write, so only pre-extracted attributes are searchable.

**Example (customer ask):**

**Log contains JSON blob in a field:**
`{ "message": "Request completed", "payload": "{\"id\":\"123\",\"items\":[{\"sku\":\"A1\"}]}" }
`

**Expected (KQL/AppInsights):**
```
| extend p = parse_json(payload)
| where tostring(p.id) == "123"
| mv-expand item = p.items
| where tostring(item.sku) == "A1"
```

**Sentry today:**
Not possible unless id, items.sku, etc. are extracted/flattened at ingestion.

**Current Limitations:**

- No query-time JSON parsing
- No nested field access inside JSON blobs
- No array expansion (mv-expand equivalent)
- No query-time string parsing/regex extraction

### Solution Brainstorm

_No response_

### Product Area

Processing