Rename "Stackmap" to "StackMap"

And "stackmap" to "stack_map".

This commit is purely mechanical.

cranelift/codegen/src/machinst/abi.rs

@@ -1,6 +1,6 @@
 //! ABI definitions.
 
-use crate::binemit::Stackmap;
+use crate::binemit::StackMap;
 use crate::ir::StackSlot;
 use crate::machinst::*;
 use crate::settings;
@@ -96,14 +96,14 @@ pub trait ABIBody {
     /// Store to a spillslot.
     fn store_spillslot(&self, slot: SpillSlot, ty: Type, from_reg: Reg) -> Self::I;
 
-    /// Generate a stackmap, given a list of spillslots and the emission state
+    /// Generate a stack map, given a list of spillslots and the emission state
     /// at a given program point (prior to emission fo the safepointing
     /// instruction).
-    fn spillslots_to_stackmap(
+    fn spillslots_to_stack_map(
         &self,
         slots: &[SpillSlot],
         state: &<Self::I as MachInstEmit>::State,
-    ) -> Stackmap;
+    ) -> StackMap;
 
     /// Generate a prologue, post-regalloc. This should include any stack
     /// frame or other setup necessary to use the other methods (`load_arg`,