gh-124697: Represent inlined comprehensions as subscopes in the symbol table

[iritkatriel]

Resolves #124697

Inlined comprehensions are now represented in the symbol table as block of a new type InlinedComprehensionBlock, which is a subscope of the enclosing scope and is interpreted
as the delta between the containing scope and the comprehension scope. Symbol lookups that
fail in the subscope continue in the containing scope.

This moves the complexity of compiling inlined comprehensions from codegen to the symbol table
construction.

It removes the smell of the compiler to modifying the symbol table in codegen.

• Issue: refactor the implementation of inlined comprehensions #124697

[read-the-docs-community]

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± library/symtable.html
± whatsnew/3.16.html
± whatsnew/changelog.html