fix(ivy): ensure NgClass does not overwrite other dir data (#31788)

We currently have a handwritten version of the Ivy directive def for NgClass so
we can switch between Ivy and View Engine behavior. This generated code needs to
be kept up-to-date with what the Ivy compiler generates.

PR 30742 recently changed `classMap` such that it now requires allocation of
host binding slots. This means that the `allocHostVars()` function must be
called in the NgClass directive def to match compiler output, but the
handwritten directive def was not updated. This caused a bug where NgClass
was inappropriately overwriting data for other directives because space was
not allocated for its values.

PR Close #31788

packages/compiler-cli/test/compliance/r3_view_compiler_styling_spec.ts

@@ -1278,6 +1278,8 @@ describe('compiler compliance: styling', () => {
            }
          };
 
+         // NOTE: IF YOU ARE CHANGING THIS COMPILER SPEC, YOU MAY NEED TO CHANGE THE DIRECTIVE
+         // DEF THAT'S HARD-CODED IN `ng_class.ts`.
          const template = `
           function ClassDirective_HostBindings(rf, ctx, elIndex) {
             if (rf & 1) {