Migrate to the new threading model more gently

[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

As pointed out by some of our testers, an app that has any amount of background processing will probably crash on basic usage when upgrading to v2.6.0.

How to reproduce

Run on develop and include in your app this minimal code:

go func() {
    w.setTitle("Crash on some systems")
}

Screenshots

No response

Example code

go func() {
    w.setTitle("Crash on some systems")
}

Fyne version

v2.6.0-pre

Go compiler version

all

Operating system and version

macOS particularly, but many variants

Additional Information

Plan:

• Where previously we had runOnMain for window handling / OS impacting code we should have a thread check that will be removed later (Moving window handling functions into a safer transition mode #5415)
• Add this same safety to common entry-points (Widget.Refresh() for one)
• Print clear warnings / errors that the thread management was not correct (Moving window handling functions into a safer transition mode #5415)
• Add a way for apps to opt out of this (potentially slow) thread checking
• Make a statement about when this migration path will be disabled (2.8?) - https://github.com/fyne-io/fyne/wiki/Threading-migration

[andydotxyz]

Linking this to the parent ticket as well #4654

[andydotxyz]

So far I have a utility function that we can use appropriately:

func EnsureMain(fn func()) {
	if build.DisableThreadChecks || IsMainGoroutine() {
		fn()
		return
	}

	// logging code here too
	fyne.Do(fn)
}

And I propose log output along the lines of:

2025/01/14 22:18:59 *** Error in Fyne call thread, this should have been called in fyne.Do ***
2025/01/14 22:18:59   At: /Users/andy/Code/Fyne/fyne/cmd/hello/main.go:21

If this looks like a good start I can open a PR for that which will avoid a lot of crashes, then we can look at how it would be applied wider and also how to disable it for the project once people have ported over

[Jacalz]

As noted in #5420, we need to wait with moving internal maps over because it will cause crashes for anyone with old code still updating elements in goroutines.

[andydotxyz]

The main points are all delivered now :)