Fix broken numeric and bignumeric type mapping in BigQuery connector

[ebyhr]

testBigNumericMapping and testNumericMapping in TestBigQueryTypeMapping keep failing.

io.trino.spi.TrinoException: Unhandled type for Int128: decimal(24,2)
	at io.trino.plugin.bigquery.BigQueryResultPageSource.appendTo(BigQueryResultPageSource.java:206)
	at io.trino.plugin.bigquery.BigQueryResultPageSource.getNextPage(BigQueryResultPageSource.java:143)
	at io.trino.operator.TableScanOperator.getOutput(TableScanOperator.java:311)
	at io.trino.operator.Driver.processInternal(Driver.java:388)
	at io.trino.operator.Driver.lambda$processFor$9(Driver.java:292)
	at io.trino.operator.Driver.tryWithLock(Driver.java:685)
	at io.trino.operator.Driver.processFor(Driver.java:285)
	at io.trino.execution.SqlTaskExecution$DriverSplitRunner.processFor(SqlTaskExecution.java:1076)
	at io.trino.execution.executor.PrioritizedSplitRunner.process(PrioritizedSplitRunner.java:163)
	at io.trino.execution.executor.TaskExecutor$TaskRunner.run(TaskExecutor.java:488)
	at io.trino.$gen.Trino_testversion____20220112_103240_2.run(Unknown Source)
	at java.base/java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1128)
	at java.base/java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:628)
	at java.base/java.lang.Thread.run(Thread.java:829)

fb88c0b introduced this bug.