RFR: 8259948: Aarch64: Add cast nodes for Aarch64 Neon backend [v4]

[Wu Yan]

On Tue, 7 Sep 2021 09:52:39 GMT, Eric Liu <eliu at openjdk.org> wrote:

>> Because @theRealELiu suggest us not to have VectorCast with bit_size less than 64 bits support.
>> In addition, we will add rules for the 4B vector, which will appear in actual situations. I'll refine the code in next commit.
>
> Byte is special here. 
> 
> Refs:
> [1] https://github.com/openjdk/jdk/blob/master/src/hotspot/share/opto/matcher.hpp#L341
> [2] https://github.com/openjdk/jdk/blob/master/src/hotspot/cpu/aarch64/aarch64.ad#L2491

We have removed it.

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PR: https://git.openjdk.java.net/jdk/pull/4839