fix(format): keep a macro-named label line whole

A label whose name is a macro expands into whatever the body is, so the
line's statement structure exists only after expansion; splitting the
label off changed clean input into a different statement sequence.  The
formatter now records the names #define'd above each line and renders
such a label line unsplit, and the crashing input joins the corpus.

Assisted-by: GLM 5.3

format/testdata/fuzz/FuzzFormatExpansionRoundTrip/3508c784782f0866

@@ -0,0 +1,2 @@
+go test fuzz v1
+string("#define A B0\"\nA:A00")