[SPARK-39759][SQL] Implement listIndexes in JDBC (H2 dialect)

[panbingkun]

What changes were proposed in this pull request?

Implementing listIndexes in DS V2 JDBC for H2 dialect.

Why are the changes needed?

This is a subtask of the V2 Index support(https://issues.apache.org/jira/browse/SPARK-36525).
It can better test the index interface locally.

This PR implements listIndexes in H2 dialect.

Does this PR introduce any user-facing change?

Yes, listIndexes in DS V2 JDBC for H2

How was this patch tested?

Update existed UT.

[panbingkun]

In fact, I found possible null pointer in the implementation of listIndexes(H2), indexComment default value is null.
However, the default value of MySQLDIalect is empty String.
@huaxingao

[panbingkun]

ping @huaxingao

[AmplabJenkins]

Can one of the admins verify this patch?

[huaxingao]

Does H2 support composite index?

[panbingkun]

Does H2 support composite index?
Yes, support

1.add follow code in beforeAll:

conn.prepareStatement(
"CREATE TABLE "test"."people1" (name TEXT(32) NOT NULL, " +
"id1 INTEGER NOT NULL, id2 INTEGER NOT NULL)")
.executeUpdate()
conn.prepareStatement("INSERT INTO "test"."people1" VALUES ('fred', 1, 1)").
executeUpdate()
conn.prepareStatement("INSERT INTO "test"."people1" VALUES ('mary', 2, 2)").
executeUpdate()

2.change UT

val loaded = Catalogs.load("h2", conf)
val jdbcTable = loaded.asInstanceOf[TableCatalog]
.loadTable(Identifier.of(Array("test"), "people1"))
.asInstanceOf[SupportsIndex]
assert(jdbcTable != null)
assert(jdbcTable.indexExists("people_index") == false)
val indexes1 = jdbcTable.listIndexes()
assert(indexes1.isEmpty)

sql(s"CREATE INDEX people_index ON TABLE h2.test.people1 (id1, id2)")
assert(jdbcTable.indexExists("people_index"))
val indexes2 = jdbcTable.listIndexes()
assert(!indexes2.isEmpty)
assert(indexes2.size == 1)
val tableIndex = indexes2.head
assert(tableIndex.indexName() == "people_index")
sql(s"DROP INDEX people_index ON TABLE h2.test.people1")
assert(jdbcTable.indexExists("people_index") == false)
val indexes3 = jdbcTable.listIndexes()
assert(indexes3.isEmpty)

3.debug view

[huaxingao]

Merged to master. Thanks @panbingkun