Various cranelift interpreter improvements (#6176)

* Remove the validate_address State trait method

It isn't used anywhere

* Expose the inner Function of a Frame

This is necessary to create your own interpreter that reuses most of
cranelift-interpreter. For example to use a different State
implementation.

* Support the symbol_value and tls_value instructions in the interpreter

cranelift/interpreter/src/frame.rs

@@ -12,7 +12,7 @@ pub(crate) type Entries = Vec<Option<DataValue>>;
 #[derive(Debug)]
 pub struct Frame<'a> {
     /// The currently executing function.
-    pub(crate) function: &'a Function,
+    function: &'a Function,
     /// The current mapping of SSA value-references to their actual values. For efficiency, each SSA value is used as an
     /// index into the Vec, meaning some slots may be unused.
     registers: Entries,
@@ -100,6 +100,11 @@ impl<'a> Frame<'a> {
     pub fn entries_mut(&mut self) -> &mut [Option<DataValue>] {
         &mut self.registers
     }
+
+    /// Accessor for the [`Function`] of this frame.
+    pub fn function(&self) -> &'a Function {
+        self.function
+    }
 }
 
 #[cfg(test)]