Add SMT2 FPA backend tests for fp.fma emission

Verify that --smt2 --fpa emits fp.fma (not bitvector encoding) for
both normal FMA operations and special cases (NaN, infinity).

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

Author: tautschnig

regression/cbmc-library/fma/test_fpa_emission.desc

@@ -0,0 +1,10 @@
+CORE smt-backend
+precision.c
+--smt2 --fpa --outfile -
+fp\.fma
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+--
+Verify that the SMT2 FPA backend emits fp.fma (not a bitvector encoding).

regression/cbmc-library/fma/test_fpa_special_emission.desc

@@ -0,0 +1,10 @@
+CORE smt-backend
+special_cases.c
+--smt2 --fpa --outfile -
+fp\.fma
+^EXIT=0$
+^SIGNAL=0$
+--
+^warning: ignoring
+--
+Verify that FMA special cases (NaN, inf) emit fp.fma via FPA backend.