Support .Select().Where() expression hoisting in LINQ

[jeremydmiller]

Summary

• Fixes V7 Select before Where no longer working #3009: .Select(x => x.Inner).Where(x => x.Value < 50) silently dropped the Where clause
• Detects post-Select Where expressions in SelectOperator and rewrites them to reference the original document type through the Select member path
• Handles both different-type selects (e.g., Target → Address) and same-type selects (e.g., Target.Inner is Target)

How it works

Due to outermost-to-innermost expression tree traversal, operators after Select in user code are processed before the Select operator. At the time SelectOperator.Apply() runs, any WhereExpressions on the current CollectionUsage are from post-Select operators and need hoisting. A PostSelectExpressionRewriter (ExpressionVisitor) replaces ParameterExpression references of the projected type with the Select body MemberExpression, e.g. y.Value > 5 becomes x.Inner.Value > 5.

Test plan

• 9 new integration tests in LinqTests/Bugs/Bug_3009_select_before_where.cs covering:
  • Different-type Select().Where()
  • Equivalence with Where().Select() (normal order)
  • Same-type Select().Where() (Target.Inner)
  • Multiple Where clauses after Select
  • String comparison in post-Select Where
  • FirstOrDefault terminal after Select().Where()
  • Count terminal after Select().Where()
  • Combined pre-Select and post-Select Where
  • Deep nested member Select (Level1.Level2) before Where
• All 1201 existing LinqTests pass (6 pre-existing failures unrelated to this change)

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