RFR: 8302518: Add missing Op_RoundDoubleMode in VectorNode::vector_operands() [v2]

[Pengfei Li]

> This is a one-line fix.
> 
> `VectorNode::vector_operands()` is a C2 function used to get a half-open range of `[start, end)` defining which operands are vectors to process. `Op_RoundDoubleMode` has two operands but only the 1st one is a vector. Its 2nd operand is the rounding mode. Missing this op results in its 2nd operand treated as a vector. It is fortunate that it hasn't caused any issue yet as the code follows just treated the 2nd input as an immediate to replicate later. If we add some check like `n->is_Vector()` for the vectorized node then, there will be issues. We should fix this potential problem.
> 
> Tested tier1.

Pengfei Li has updated the pull request incrementally with one additional commit since the last revision:

  Add rotate shift opcodes

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Changes:
  - all: https://git.openjdk.org/jdk/pull/12584/files
  - new: https://git.openjdk.org/jdk/pull/12584/files/53038661..47629d03

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=12584&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=12584&range=00-01

  Stats: 7 lines in 1 file changed: 7 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/12584.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/12584/head:pull/12584

PR: https://git.openjdk.org/jdk/pull/12584