[SPARK-53840][SQL] Add AS JSON output support for SHOW TABLES and SHOW TABLE EXTENDED

[ayushbilala]

What changes were proposed in this pull request?

Support SHOW TABLES ... [AS JSON] and SHOW TABLE EXTENDED ... [AS JSON] to optionally display table listing metadata in JSON format.
SQL syntax:

SHOW TABLES [(IN|FROM) database_name] [[LIKE] pattern] [AS JSON]
SHOW TABLE EXTENDED [(IN|FROM) database_name] LIKE pattern [AS JSON]

Output: json_metadata: String

SHOW TABLES AS JSON:
{"tables":[{"name":"t1","namespace":["db"],"isTemporary":false}]}

SHOW TABLE EXTENDED ... AS JSON additionally includes catalog and type:
{"tables":[{"catalog":"spark_catalog","namespace":["db"],"name":"t1","type":"TABLE","isTemporary":false}]}

Why are the changes needed?

The existing text-based output of SHOW TABLES requires fragile string parsing for programmatic consumption.
A structured JSON format provides a stable, machine-readable contract for tooling and automation.

Does this PR introduce any user-facing change?

Yes. Two new SQL syntax variants that return JSON output. Existing commands without AS JSON are unaffected.
SHOW TABLE EXTENDED with both PARTITION and AS JSON is explicitly rejected.

How was this patch tested?

• Parser tests in ShowTablesParserSuite for all AS JSON variants and the PARTITION + AS JSON error case.
• Execution tests in ShowTablesSuiteBase covering JSON schema validation, empty databases, EXTENDED output, and temp view inclusion.
• Manual verification in spark-shell

Was this patch authored or co-authored using generative AI tooling?

No

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Continuation of #54824 (closed to move off fork master branch for CI)

[cloud-fan]

failed tests unrelated, thanks, merging to master/4.x!