[DebugMetadata][DwarfDebug] Support function-local types in lexical block scopes (4/7)

RFC https://discourse.llvm.org/t/rfc-dwarfdebug-fix-and-improve-handling-imported-entities-types-and-static-local-in-subprogram-and-lexical-block-scopes/68544



Similar to imported declarations, the patch tracks function-local types in
DISubprogram's 'retainedNodes' field. DwarfDebug is adjusted in accordance with
the aforementioned metadata change and provided a support of function-local
types scoped within a lexical block.

The patch assumes that DICompileUnit's 'enums field' no longer tracks local
types and DwarfDebug would assert if any locally-scoped types get placed there.

Reviewed By: jmmartinez
Authored-by: Kristina Bessonova <kbessonova@accesssoftek.com>
Differential Revision: https://reviews.llvm.org/D144006