Extract map_theoryt base class from arrayst

Separate map-theoretic reasoning (index tracking, equality tracking,
Ackermann constraints, read-over-weakeq, extensionality, CDCL(T)
propagation, constraint counting) from array-specific encoding
(with/if/of/comprehension constraints, lazy selects, 2D inlining).

Inheritance chain: arrayst -> map_theoryt -> equalityt -> prop_conv_solvert

Co-authored-by: Kiro <kiro-agent@users.noreply.github.com>

Author: tautschnig

src/solvers/Makefile

@@ -140,6 +140,7 @@ SRC = $(BOOLEFORCE_SRC) \
       flattening/bv_utils.cpp \
       flattening/c_bit_field_replacement_type.cpp \
       flattening/equality.cpp \
+      flattening/map_theory.cpp \
       flattening/pointer_logic.cpp \
       floatbv/float_bv.cpp \
       floatbv/float_utils.cpp \