Apply HiDPI mode on GUI setup

[GabrieleC]

Description

Apply HiDPI fonts on GUI startup according to jmeter.hidpi.mode and jmeter.hidpi.scale.factor properties.

Motivation and Context

Useful to avoid setting zoom scale manually every time GUI is started.

How Has This Been Tested?

Tested on Windows 11:

• open JMeter and notice the initial zoom level
• close JMeter and set jmeter.hidpi.mode=true and jmeter.hidpi.scale.factor=2 in jmeter.properties
• open JMeter and notice the greater zoom level applied at startup

Types of changes

• New feature (non-breaking change which adds functionality)

Checklist:

• [x] My code follows the [code style][style-guide] of this project.
• [ ] I have updated the documentation accordingly.