Rollup merge of #83519 - oli-obk:assign_shrink_your_normal_code, r=pnkfelix

Implement a lint that highlights all moves larger than a configured limit

Tracking issue: #83518
[MCP 420](https://github.com/rust-lang/compiler-team/issues/420) still ~blazing~ in progress

r? ```@pnkfelix```

The main open issue I see with this minimal impl of the feature is that the lint is immediately "stable" (so it can be named on stable), even if it is never executed on stable. I don't think we have the concept of unstable lint names or hiding lint names without an active feature gate, so that would be a bigger change.

compiler/rustc_session/src/session.rs

@@ -83,6 +83,12 @@ impl Limit {
     }
 }
 
+impl From<usize> for Limit {
+    fn from(value: usize) -> Self {
+        Self::new(value)
+    }
+}
+
 impl fmt::Display for Limit {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(f, "{}", self.0)
@@ -143,6 +149,10 @@ pub struct Session {
     /// operations such as auto-dereference and monomorphization.
     pub recursion_limit: OnceCell<Limit>,
 
+    /// The size at which the `large_assignments` lint starts
+    /// being emitted.
+    pub move_size_limit: OnceCell<usize>,
+
     /// The maximum length of types during monomorphization.
     pub type_length_limit: OnceCell<Limit>,
 
@@ -352,6 +362,11 @@ impl Session {
         self.recursion_limit.get().copied().unwrap()
     }
 
+    #[inline]
+    pub fn move_size_limit(&self) -> usize {
+        self.move_size_limit.get().copied().unwrap()
+    }
+
     #[inline]
     pub fn type_length_limit(&self) -> Limit {
         self.type_length_limit.get().copied().unwrap()
@@ -1414,6 +1429,7 @@ pub fn build_session(
         features: OnceCell::new(),
         lint_store: OnceCell::new(),
         recursion_limit: OnceCell::new(),
+        move_size_limit: OnceCell::new(),
         type_length_limit: OnceCell::new(),
         const_eval_limit: OnceCell::new(),
         incr_comp_session: OneThread::new(RefCell::new(IncrCompSession::NotInitialized)),