Preserve value numbers in gtSetEvalOrder

[JosephTremoulet]

There was already code to preserve the value number during global CSE, but
value numbers remain relevant through assertion prop, so this changes the
code to simply always pass the PRESERVE_VN flag.

[JosephTremoulet]

This resolves a side issue getting in the way of #10050.

Jit-diff reports:

Summary:
(Note: Lower is better)
Total bytes of diff: -3039 (0.00 % of base)
    diff is an improvement.
Total byte diff includes 0 bytes from reconciling methods
        Base had    0 unique methods,        0 unique bytes
        Diff had    0 unique methods,        0 unique bytes
Top file regressions by size (bytes):
           9 : JIT\Directed\Arrays\Complex1\Complex1.dasm (0.46 % of base)
           8 : JIT\Directed\Arrays\Simple1\Simple1.dasm (0.42 % of base)
Top file improvements by size (bytes):
        -522 : Microsoft.CodeAnalysis.CSharp.dasm (-0.02 % of base)
        -259 : System.Private.CoreLib.dasm (-0.01 % of base)
        -152 : Microsoft.CodeAnalysis.dasm (-0.02 % of base)
        -130 : JIT\Performance\CodeQuality\SciMark\SciMark\SciMark.dasm (-0.80 % of base)
        -114 : System.Linq.Expressions.dasm (-0.02 % of base)
75 total files with size differences (73 improved, 2 regressed).
Top method regessions by size (bytes):
           9 : JIT\Directed\Arrays\Complex1\Complex1.dasm - Complex_Array_Test:Main(ref):int
           8 : System.Private.CoreLib.dasm - RuntimeType:InvokeMember(ref,int,ref,ref,ref,ref,ref,ref):ref:this
           8 : JIT\Directed\Arrays\Simple1\Simple1.dasm - Simple_Array_Test:Main(ref):int
Top method improvements by size (bytes):
         -76 : Microsoft.CodeAnalysis.dasm - CommonReferenceManager`2:ReuseAssemblySymbolsWithNoPiaLocalTypes(ref,ref,struct,int):bool:this
         -74 : Microsoft.CodeAnalysis.CSharp.dasm - ReferenceManager:SetupReferencesForFileAssembly(ref,ref,int,byref,ref)
         -42 : Microsoft.CodeAnalysis.CSharp.dasm - NamedTypeSymbol:EqualsComplicatedCases(ref,bool,bool):bool:this
         -42 : System.Private.Uri.dasm - UriHelper:MatchUTF8Sequence(long,ref,byref,ref,int,ref,int,bool,bool)
         -40 : System.Linq.Expressions.dasm - Expression:ValidateLambdaArgs(ref,byref,ref,ref)
135 total methods with size differences (132 improved, 3 regressed).

I looked at the regressions; they are cases where the additional assertion's we're now tracking make us bump up against our assertion index limit. The improvements are cases of redundant code being removed by assertion prop, as you'd expect.

I'm not planning to merge this until after the 2.0 stabilization.

/cc @dotnet/jit-contrib

[erozenfeld]

LGTM

[pgavlin]

LGTM.

[briansull]

LGTM