Allow matplotlib.use calls to intersperse imports (#9094)

This PR allows `matplotlib.use` calls to intersperse imports without
triggering `E402`. This is a pragmatic choice as it's common to require
`matplotlib.use` calls prior to importing from within `matplotlib`
itself.

Closes https://github.com/astral-sh/ruff/issues/9091.

crates/ruff_python_semantic/src/analyze/imports.rs

@@ -35,3 +35,21 @@ pub fn is_sys_path_modification(stmt: &Stmt, semantic: &SemanticModel) -> bool {
             )
         })
 }
+
+/// Returns `true` if a [`Stmt`] is a `matplotlib.use` activation, as in:
+/// ```python
+/// import matplotlib
+///
+/// matplotlib.use("Agg")
+/// ```
+pub fn is_matplotlib_activation(stmt: &Stmt, semantic: &SemanticModel) -> bool {
+    let Stmt::Expr(ast::StmtExpr { value, range: _ }) = stmt else {
+        return false;
+    };
+    let Expr::Call(ast::ExprCall { func, .. }) = value.as_ref() else {
+        return false;
+    };
+    semantic
+        .resolve_call_path(func.as_ref())
+        .is_some_and(|call_path| matches!(call_path.as_slice(), ["matplotlib", "use"]))
+}