Include terminators in instance size estimate

For example, drop glue generated for struct below, doesn't have any
statements, only terminators. Previously it received an estimate of 0,
the new estimate is 13 (6+5 drop terminators, +1 resume, +1 return).

struct S {
    a: String,
    b: String,
    c: String,
    d: String,
    e: String,
    f: String,
}

Originally reported in rust-lang#69382 (comment)

compiler/rustc_ty_utils/src/ty.rs

@@ -402,7 +402,7 @@ fn instance_def_size_estimate<'tcx>(
     match instance_def {
         InstanceDef::Item(..) | InstanceDef::DropGlue(..) => {
             let mir = tcx.instance_mir(instance_def);
-            mir.basic_blocks().iter().map(|bb| bb.statements.len()).sum()
+            mir.basic_blocks().iter().map(|bb| bb.statements.len() + 1).sum()
         }
         // Estimate the size of other compiler-generated shims to be 1.
         _ => 1,