Fix #2445 Add missing WindowMaximizeButtonHint to window flags

[ebuzerdrmz44]

Description

The main window's maximize button in the title bar does not work. This is because setWindowFlags only sets WindowCloseButtonHint and WindowMinimizeButtonHint, missing WindowMaximizeButtonHint. I've added it.

Related Issue

#2445

Motivation and Context

To maximize the window.

How Has This Been Tested?

Manually verified that the maximize button in the title bar becomes functional after the change.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

I provide my contribution under the terms of the license of this repository and I affirm the Developer Certificate of Origin.