RFR: 8297238: RISC-V: Unifying predicates for vector type matching in c2

[Gui Cao]

Hi,

In the vector type predicate matching process of riscv, n->bottom_type()->is_vect()->element_basic_type() is used in some places to get the data type, and Matcher::vector_element_basic_type(n) is used in some places to get the data type, In fact, Matcher::vector_element_basic_type(n) is the function encapsulation form of n->bottom_type()->is_vect()->element_basic_type(), here Matcher::vector_element_basic_type(n) is used uniformly to get the data type

Please take a look and have some reviews. Thanks a lot.

## Testing:
- hotspot and jdk tier1 without new failures (release with UseRVV on QEMU)
- test/jdk/jdk/incubator/vector/* (fastdebug/release with UseRVV on QEMU)

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Commit messages:
 - Unifying predicates for vector type matching in c2

Changes: https://git.openjdk.org/jdk/pull/11239/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=11239&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8297238
  Stats: 18 lines in 1 file changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/11239.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/11239/head:pull/11239

PR: https://git.openjdk.org/jdk/pull/11239