arch: common: sw_isr: make sure that the table index is within range

Assert that the `local_irq` of each levels should only ranges
from `0` to `CONFIG_MAX_IRQ_PER_AGGREGATOR`, so that it doesn't
overflow the other aggregators.

Also, assert that the output of `z_get_sw_isr_table_idx` shouldn't
overflow the ISR table.

Update the `sw_isr_table` tests to test the range of
`CONFIG_MAX_IRQ_PER_AGGREGATOR` instead of the entire range of
level bits.

Signed-off-by: Yong Cong Sin <ycsin@meta.com>