Misc cleanups (#5014)

* Replace resize+copy_from_slice with extend_from_slice

Vec::resize initializes the new space, which is wasted effort if we're
just going to call `copy_from_slice` on it immediately afterward. Using
`extend_from_slice` is simpler, and very slightly faster.

If the new size were bigger than the buffer we're copying from, then it
would make sense to initialize the excess. But it isn't: it's always
exactly the same size.

* Move helpers from Context to CompiledCode

These methods only use information from Context::compiled_code, so they
should live on CompiledCode instead.

* Remove an unnecessary #[cfg_attr]

There are other uses of `#[allow(clippy::too_many_arguments)]` in this
file, so apparently it doesn't need to be guarded by the "cargo-clippy"
feature.

* Fix a few comments

Two of these were wrong/misleading:

- `FunctionBuilder::new` does not clear the provided func_ctx. It does
  debug-assert that the context is already clear, but I don't think
  that's worth a comment.

- `switch_to_block` does not "create values for the arguments." That's
  done by the combination of `append_block_params_for_function_params`
  and `declare_wasm_parameters`.

* wasmtime-cranelift: Misc cleanups

The main change is to use the `CompiledCode` reference we already had
instead of getting it out of `Context` repeatedly. This removes a bunch
of `unwrap()` calls.

* wasmtime-cranelift: Factor out uncached compile

cranelift/codegen/src/isa/mod.rs

@@ -56,7 +56,7 @@ use crate::CodegenResult;
 use alloc::{boxed::Box, vec::Vec};
 use core::fmt;
 use core::fmt::{Debug, Formatter};
-use target_lexicon::{triple, Architecture, OperatingSystem, PointerWidth, Triple};
+use target_lexicon::{triple, Architecture, PointerWidth, Triple};
 
 // This module is made public here for benchmarking purposes. No guarantees are
 // made regarding API stability.
@@ -360,18 +360,6 @@ impl<'a> dyn TargetIsa + 'a {
             pointer_width: self.pointer_width(),
         }
     }
-
-    /// Returns the flavor of unwind information emitted for this target.
-    pub(crate) fn unwind_info_kind(&self) -> UnwindInfoKind {
-        match self.triple().operating_system {
-            #[cfg(feature = "unwind")]
-            OperatingSystem::Windows => UnwindInfoKind::Windows,
-            #[cfg(feature = "unwind")]
-            _ => UnwindInfoKind::SystemV,
-            #[cfg(not(feature = "unwind"))]
-            _ => UnwindInfoKind::None,
-        }
-    }
 }
 
 impl Debug for &dyn TargetIsa {