Extend getMaxbits to handle Block type

[xuruiyang2002]

There is a need to extend the getMaxBits to handle the Block.

For example, wasm-opt (95808a7) cannot optimize the following code snippet

   (i32.and
    (i32.load
     (i32.const 0)
    )
    (block (result i32)
     (i32.store
      (i32.const 0)
      (i32.const 0)
     )
     (i32.const 0)
    )

to zero, the root cause is that getMaxBits fails to deal with the block.

Fixes: #7559

[xuruiyang2002]

Current PR is to just implement the getMaxBits for Block.

As discussed in #7559, should we bother to introduce the getFallthrough? In doing so, we'd also modify the API and the references and tests. What's more, invoking getFallthrough maybe prohibited. Because bits.h is included by properties.h before the getFallthrough function itself is defined within properties.h, which thus making it invisible at the point of the call.

[xuruiyang2002]

UPDATE: I've fuzzing for about three hour, and all is well.