Exasol dialect: Add support for JSON_EXTRACT

[nnamdi16]

Description

SQLGlot currently does not fully support the JSON_EXTRACT function in the Exasol dialect.

Parent issue: tobymao#6695

---

Example

SELECT JSON_EXTRACT(data, '$.user.name') FROM users;

---

Current Behaviour

SQLGlot does not properly parse and generate JSON_EXTRACT for Exasol.

---

Expected Behaviour

SQLGlot should correctly support JSON_EXTRACT in Exasol.

---

Proposed solution

Add:
• Parser support
• Expression support
• Generator support

for JSON_EXTRACT in the Exasol dialect.

[nnamdi16]

The issue has been resolved and merged tobymao#7098