Set UnusedValue correctly for the operands of ARR_ADDR/BOX

[SingleAccretion]

#70398 exposed a previously unseen case of a top-level ARR_ADDR node:

***** BB05
STMT00032 ( ??? ... 0x0E9 )
N010 ( 10,  9) [001316] -A---------                         *  ARR_ADDR  byref ubyte[] $301
N009 ( 10,  9) [001317] -A-----N---                         \--*  ADD       byref  $2ca
N007 ( 10,  9) [002064] -A---------                            +--*  COMMA     byref  $2c0
N005 (  7,  7) [002062] -A------R--                            |  +--*  ASG       byref  $VN.Void
N004 (  3,  2) [002061] D------N---                            |  |  +--*  LCL_VAR   byref  V70 cse3         d:1 $2c0
N003 (  3,  4) [001318] -----------                            |  |  \--*  ADD       byref  $2c0
N001 (  1,  1) [001319] -----------                            |  |     +--*  LCL_VAR   ref    V03 loc3         u:2 $241
N002 (  1,  2) [001320] -----------                            |  |     \--*  CNS_INT   long   16 $1c1
N006 (  3,  2) [002063] -----------                            |  \--*  LCL_VAR   byref  V70 cse3         u:1 $2c0
N008 (  1,  2) [002085] -----------                            \--*  CNS_INT   long   1 $1c4

When we rationalize these nodes, we replace them with their operands. That handling was not quite complete, resulting in some missed UnusedValue flags.

Fixes #70466.

No diffs as expected.

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Issue Details

---

#70398 exposed a previously unseen case of top-level ARR_ADDR nodes:

***** BB05
STMT00032 ( ??? ... 0x0E9 )
N010 ( 10,  9) [001316] -A---------                         *  ARR_ADDR  byref ubyte[] $301
N009 ( 10,  9) [001317] -A-----N---                         \--*  ADD       byref  $2ca
N007 ( 10,  9) [002064] -A---------                            +--*  COMMA     byref  $2c0
N005 (  7,  7) [002062] -A------R--                            |  +--*  ASG       byref  $VN.Void
N004 (  3,  2) [002061] D------N---                            |  |  +--*  LCL_VAR   byref  V70 cse3         d:1 $2c0
N003 (  3,  4) [001318] -----------                            |  |  \--*  ADD       byref  $2c0
N001 (  1,  1) [001319] -----------                            |  |     +--*  LCL_VAR   ref    V03 loc3         u:2 $241
N002 (  1,  2) [001320] -----------                            |  |     \--*  CNS_INT   long   16 $1c1
N006 (  3,  2) [002063] -----------                            |  \--*  LCL_VAR   byref  V70 cse3         u:1 $2c0
N008 (  1,  2) [002085] -----------                            \--*  CNS_INT   long   1 $1c4

When we rationalize these nodes, we replace them with their operands. That handling was not quite complete, resulting in some missed UnusedValue flags.

Fixes #70466.

Author:	SingleAccretion
Assignees:	-
Labels:	area-CodeGen-coreclr
Milestone:	-

[SingleAccretion]

@dotnet/jit-contrib

Fixing stress.