Fix editor loading state shows flash of incorrect rendering mode

[Mayank-Tripathi32]

attempt fix #69088
related #68110

What?

Address editor rendering mode initialization issue identified in #69088.

Why?

Current implementation delays setting default rendering mode until template loads, causing "post-only" state to be set temporarily.

How?

Modify default mode initialization to:

	defaultMode: hasDefaultMode ? _defaultMode : 'post-only';

This maintains mode validation while removing template dependency.

Testing Instructions

• Open editor with a template-supported post type
• Verify rendering does not flash the "post-only" page view.
• Confirm mode switches correctly between post-only and template-locked states
• Test with various post types to ensure proper mode initialization

ScreenCast

loading.issue.mov

[Mayank-Tripathi32]

	[ post.type, hasTemplate ]

Also, I noticed a bit of performance diff if I removed hasTemplate, not sure if it can measured.