swf: Store register count from DefineFunction2

Also update avm1::Function to use register_count.

core/src/avm1/function.rs

@@ -112,7 +112,7 @@ impl<'gc> Avm1Function<'gc> {
             swf_version,
             data: actions,
             name,
-            register_count: swf_function.params.capacity() as u8,
+            register_count: swf_function.register_count,
             preload_parent: swf_function.preload_parent,
             preload_root: swf_function.preload_root,
             suppress_super: swf_function.suppress_super,

swf/src/avm1/read.rs

@@ -325,9 +325,9 @@ impl<'a> Reader<'a> {
     fn read_define_function_2(&mut self, action_length: &mut usize) -> Result<Action<'a>> {
         let name = self.read_c_string()?;
         let num_params = self.read_u16()?;
-        let num_registers = self.read_u8()?; // Number of registers
+        let register_count = self.read_u8()?; // Number of registers
         let flags = self.read_u16()?;
-        let mut params = Vec::with_capacity(num_params as usize + num_registers as usize);
+        let mut params = Vec::with_capacity(num_params as usize);
         for _ in 0..num_params {
             let register = self.read_u8()?;
             params.push(FunctionParam {
@@ -341,6 +341,7 @@ impl<'a> Reader<'a> {
         Ok(Action::DefineFunction2(Function {
             name,
             params,
+            register_count,
             preload_global: flags & 0b1_00000000 != 0,
             preload_parent: flags & 0b10000000 != 0,
             preload_root: flags & 0b1000000 != 0,

swf/src/avm1/types.rs

@@ -153,6 +153,7 @@ pub enum SendVarsMethod {
 #[derive(Clone, Debug, PartialEq)]
 pub struct Function<'a> {
     pub name: &'a str,
+    pub register_count: u8,
     pub params: Vec<FunctionParam<'a>>,
     pub preload_parent: bool,
     pub preload_root: bool,

swf/src/avm1/write.rs

@@ -77,15 +77,10 @@ impl<W: Write> Writer<W> {
                         .map(|p| p.name.len() + 2)
                         .sum::<usize>()
                     + 4;
-                let num_registers = function
-                    .params
-                    .iter()
-                    .map(|p| if p.register_index.is_none() { 1 } else { 0 })
-                    .sum();
                 self.write_action_header(OpCode::DefineFunction2, len)?;
                 self.write_c_string(&function.name)?;
                 self.write_u16(function.params.len() as u16)?;
-                self.write_u8(num_registers)?;
+                self.write_u8(function.register_count)?;
                 let flags = if function.preload_global {
                     0b1_00000000
                 } else {