Fix #3952: decompile VB.NET anonymous types and queries to valid C#

[siegfriedpammer]

Fixes #3952.

The bug

Two predicates disagreed about what a compiler-generated name looks like:

• SRMExtensions.IsGeneratedName (metadata level) counts a $ in the name, so
  SRMExtensions.IsAnonymousType matched VB$AnonymousType_* and MemberIsHidden
  dropped the definitions from the output.
• NRExtensions.HasGeneratedName(IType) (type system level) only looked for <, so
  NRExtensions.IsAnonymousType returned false and none of the anonymous-type
  translations in CallBuilder/ExpressionBuilder fired.

VB assemblies therefore lost the type definitions and kept the raw metadata names at
every use site — output that cannot be recompiled, since $ is not a legal C# identifier
character.

The fix

1. One shared predicate for both levels, so they cannot drift apart again. The
   metadata-level behaviour is kept exactly as it was: counting every name that merely
   contains < would newly capture explicit implementations of generic interface members.
2. VB transparent identifiers. The VB compiler carries query range variables in
   $VB$It, $VB$It1, $VB$It2 and $VB$ItAnonymous (Roslyn's GeneratedNameConstants),
   the counterpart to C#'s <>h__TransparentIdentifier. Unrecognized, they survived into
   the output and left the queries uncompilable even once the anonymous types were fixed.

Without the second change the first one alone still yields invalid identifiers for every VB
query with more than one range variable, which is the shape the reported assembly is full of.

Effect

A VB From i In items Let square = i * i Where square > 4 Select i, square went from

IEnumerable<VB$AnonymousType_3<int, int>> enumerable = from i in items
    select new VB$AnonymousType_3<int, int>(i, checked(i * i)) into $VB$It
    where $VB$It.square > 4
    select new VB$AnonymousType_3<int, int>($VB$It.i, $VB$It.square);

to

var enumerable = from i in items
                 let square = checked(i * i)
                 where square > 4
                 select new { i, square };

On the assembly from the issue (QuartzNetWebConsole.Views 1.0.2) every VB$AnonymousType_*
reference is gone.

Tests

New VBPretty/VBAnonymousTypes fixture (20 configurations) covering mutable and Key
anonymous types, an anonymous type as an argument, and Select/Let+Where/Join/Order By
queries. Committed fixtures-first: the expected output fails on the first commit and passes on
the last. Full ICSharpCode.Decompiler.Tests suite green (3314 passed, 46 skipped, 0 failed).

The Roslyn 2.10 / .NET Core 2.2 configuration is branched with #if: there the query operator
calls are not restored to extension-method syntax, so no query expression is formed at all.
That is a pre-existing, config-specific gap unrelated to this change.

Deliberately not in scope

• VB$AnonymousDelegate_* types (already called out in the issue as separate work). These
  are not a VB-only construct: a natural-typed C# lambda or method group that Func/Action
  cannot express makes Roslyn synthesize a delegate type too, and decompiling those is what
  the natural-type-lambdas-methods branch adds. Its IsAnonymousDelegate predicate matches
  on Name.Contains("AnonymousDelegate") through the same HasGeneratedName() this PR fixes,
  and VB's synthesized delegates satisfy its other conditions as well (empty namespace,
  TypeKind.Delegate, [CompilerGenerated]), so the two compose: this PR is what makes that
  machinery reachable for VB rather than something that has to be duplicated for it.
• Transparent identifiers that survive because the query transform bails, e.g. for lambdas
  with statement bodies (common in VB XML-literal code). This is not VB-specific: with
  QueryExpressions disabled, C# output emits 35 <>h__TransparentIdentifier references
  for the existing QueryExpressions fixture today. ILSpy applies EscapeInvalidIdentifiers
  only in the test harness, not in the default pipeline.
• VB closure display classes (_Closure$__N-M, $VB$Local_*) are still not recognized as
  such.

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This pull request was prepared by an AI agent (Claude) on Siegfried's behalf.

[siegfriedpammer]

Use if + return for readability