capture rust closures as function textobjects

Closures like

    iter.map(|a| a + 1)

Are sort-of functions, so `]f` or `maf` or `mif` can apply to them
as well as named function definitions.

runtime/queries/rust/textobjects.scm

@@ -7,6 +7,8 @@
   (function_item
     body: (_) @function.inside)) @function.around
 
+(closure_expression body: (_) @function.inside) @function.around
+
 (
   [
     (attribute_item)+