fix: PlaceholderText may not display promptly under certain circumstances

[textGamex]

Pull request type

Please check the type of change your PR introduces:

• Update
• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes

What is the current behavior?

When we set PlaceholderEnabled from false to true, if the Text is empty, the PlaceholderText will not display immediately; it will only appear after the OnTextChanged method is triggered.

Issue Number: N/A

What is the new behavior?

• A new callback function, OnPlaceholderEnabledChanged, has been added. When PlaceholderEnabled is set from false to true, if the Text is empty, the PlaceholderText will be displayed immediately, and vice versa.

Other information