fix: [fontcolorwidget] Fix font selection and display issues

[Kakueeen]

Fixed font selection and display issues in FontColorWidget by:

• Making font combo box non-editable to prevent invalid font selections
• Using currentText() instead of currentFont().family() for more reliable
  font name retrieval
• Ensuring consistent font name handling across the widget

The changes improve font selection reliability and prevent potential
issues with font family name mismatches.

Log: Fix font selection and display issues in FontColorWidget

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在pointSizesForSelectedFont函数中，使用fontComboBox->currentText()代替fontComboBox->currentFont().family()可能会导致问题，因为currentText()返回的是用户输入的文本，而currentFont().family()返回的是当前选中的字体家族名称。这可能会导致QFontDatabase::pointSizes函数无法正确获取字体大小列表。
• 在setUserConfig和getUserConfig函数中，使用currentText()代替currentFont().family()可能会导致配置保存和加载时出现不一致，因为用户输入的文本可能不一定是有效的字体家族名称。

是否建议立即修改:

• 是

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Kakueeen, LiHua000
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