Custom fonts use memory that is never freed

[andydotxyz]

Checklist

• I have searched the issue tracker for open issues that relate to the same problem, before opening a new one.
• This issue only relates to a single bug. I will open new issues for any other problems.

Describe the bug

Set a font on Text.FontSource to display some text. Then remove this text.
Memory is never cleared out of the font cache.

How to reproduce

As above

Screenshots

No response

Example code

	text1.FontSource, _ = fyne.LoadResourceFromPath("./WorkSans-Black.ttf")

Fyne version

v2.5.0-pre

Go compiler version

1.21

Operating system and version

all

Additional Information

No response

[dweymouth]

Just adding a note that this applies to fonts automatically loaded by Fyne from the OS too - although in this case it is bounded since at most one per Unicode script per style is loaded. When a fix for this is implemented we should make sure it covers the auto-loaded OS fonts that have not been used in awhile too.