JIT: fix recursive inline checking

[AndyAyersMS]

We were not setting m_Code in the root inline context, and so were
sometimes allowing one level of recursive inlining.

[AndyAyersMS]

@dotnet/jit-contrib PTAL

Minimal FX diffs.

We might want to consider recursive inlining someday, but for now we won't do it unless methods have AggressiveInlining.

Found this while looking at test cases for #33529.

PMI CodeSize Diffs for System.Private.CoreLib.dll, framework assemblies for x64 default jit
Summary of Code Size diffs:
(Lower is better)
Total bytes of diff: -434 (-0.00% of base)
    diff is an improvement.
Top file regressions (bytes):
          11 : System.Private.Xml.dasm (0.00% of base)
Top file improvements (bytes):
        -248 : System.Collections.Immutable.dasm (-0.02% of base)
        -146 : Microsoft.CodeAnalysis.VisualBasic.dasm (-0.00% of base)
         -51 : Microsoft.CodeAnalysis.CSharp.dasm (-0.00% of base)
4 total files with Code Size differences (3 improved, 1 regressed), 260 unchanged.
Top method regressions (bytes):
          11 (20.75% of base) : System.Private.Xml.dasm - XmlUntypedStringConverter:.ctor(bool):this
Top method improvements (bytes):
        -248 (-36.15% of base) : System.Collections.Immutable.dasm - Node:Add(Vector`1):Node:this
         -68 (-27.87% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Enumerator:PushToken(SyntaxToken):this
         -51 (-35.66% of base) : Microsoft.CodeAnalysis.CSharp.dasm - SourceMemberMethodSymbol:ForceComplete(SourceLocation,CancellationToken):this
         -46 (-23.96% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Enumerator:Push(GreenNode):this
         -32 (-35.56% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - TypeSubstitution:AddPairsIncludingParentToBuilder(ArrayBuilder`1):this
Top method regressions (percentages):
          11 (20.75% of base) : System.Private.Xml.dasm - XmlUntypedStringConverter:.ctor(bool):this
Top method improvements (percentages):
        -248 (-36.15% of base) : System.Collections.Immutable.dasm - Node:Add(Vector`1):Node:this
         -51 (-35.66% of base) : Microsoft.CodeAnalysis.CSharp.dasm - SourceMemberMethodSymbol:ForceComplete(SourceLocation,CancellationToken):this
         -32 (-35.56% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - TypeSubstitution:AddPairsIncludingParentToBuilder(ArrayBuilder`1):this
         -68 (-27.87% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Enumerator:PushToken(SyntaxToken):this
         -46 (-23.96% of base) : Microsoft.CodeAnalysis.VisualBasic.dasm - Enumerator:Push(GreenNode):this
6 total methods with Code Size differences (5 improved, 1 regressed), 243784 unchanged.

[erozenfeld]

LGTM