[FEATURE] Controlled finalization for GPU-bound objects

[kekekeks]

Problem:

While most of the SkiaSharp objects can be safely disposed from any thread, GPU bound ones need the corresponding GPU context to be active on disposing thread. It's fine as long as the object lifetime is controlled by application, but Dispose might be called from the finalizer thread in following cases:

1. Main has exited
2. Environment.Exit(...) is called
3. Object was somehow leaked and collected by GC without being properly disposed

Libraries using SkiaSharp can deal with the third one by thoroughly controlling the object lifetimes, but unfortunately have no control over the application control flow. That leads to crashes such as AvaloniaUI/Avalonia#4423

Proposed solution:

Instead of calling Dispose directly, call a user-specified callback that could properly enqueue the object for disposal on a proper thread or make the GPU context to be current. Such callback should be specified on object creation, e. g.

public static SKSurface Create (GRContext context, bool budgeted, SKImageInfo info, Action<Action> disposeCallback)

Finalizer should do something like this:

~SKSurface()
{
  if(_disposeCallback != null)
    _disposeCallback(() => Dispose(false));
  else
    Dispose(false);
}

[ltetak]

We have a lot of crashes in Avalonia on mac when closing tooltips. This is the native stack trace (shortened). Can this be the same reason described above?
I did one PR in Avalonia where it fixes SKFont instance (Disposed on app exit so the workaround was to disable the finalizer. This can't be used everywhere.)
AvaloniaUI/Avalonia#7887
@kekekeks

Exception Type:        EXC_BAD_ACCESS (SIGSEGV)
Exception Codes:       KERN_INVALID_ADDRESS at 0x0000000000000028
Exception Note:        EXC_CORPSE_NOTIFY

Termination Signal:    Segmentation fault: 11
Termination Reason:    Namespace SIGNAL, Code 0xb
Terminating Process:   exc handler [8893]

VM Regions Near 0x28:
--> 
    __TEXT                      103869000-103879000    [   64K] r-x/r-x SM=COW  /Applications/Synergy Editor 10.4.0.210 Staging Beta Green.app/Contents/MacOS/Synergy.Editor.Avalonia.Mac

Thread 0 Crashed:: Dispatch queue: com.apple.main-thread
0   libSkiaSharp.dylib            	0x000000010948d566 0x1091dd000 + 2819430
1   libSkiaSharp.dylib            	0x00000001094a99e5 0x1091dd000 + 2935269
2   libSkiaSharp.dylib            	0x00000001094bea4d 0x1091dd000 + 3021389
3   libSkiaSharp.dylib            	0x00000001094c01bb 0x1091dd000 + 3027387
4   libSkiaSharp.dylib            	0x000000010949c09e 0x1091dd000 + 2879646
5   libSkiaSharp.dylib            	0x000000010956eed7 0x1091dd000 + 3743447
6   libSkiaSharp.dylib            	0x000000010920f944 0x1091dd000 + 207172
7   libSkiaSharp.dylib            	0x000000010920f5b9 0x1091dd000 + 206265
8   libSkiaSharp.dylib            	0x000000010920f96e 0x1091dd000 + 207214
9   libSkiaSharp.dylib            	0x000000010957c0a1 0x1091dd000 + 3797153
10  ???                           	0x0000000110b831a3 0 + 4575474083
11  ???                           	0x0000000110b6f0ec 0 + 4575391980
12  ???                           	0x00000001116b4eee 0 + 4587212526
13  ???                           	0x000000010fd764e2 0 + 4560741602
14  ???                           	0x0000000110b96b69 0 + 4575554409
15  ???                           	0x0000000111797048 0 + 4588138568
16  ???                           	0x0000000111796ed7 0 + 4588138199
17  ???                           	0x0000000111796b3a 0 + 4588137274
18  ???                           	0x00000001117967cf 0 + 4588136399
19  ???                           	0x00000001117964f5 0 + 4588135669
20  ???                           	0x0000000111796389 0 + 4588135305
21  ???                           	0x00000001117962ae 0 + 4588135086
22  ???                           	0x000000010e9773d4 0 + 4539773908
23  libAvaloniaNative.dylib       	0x000000010591a79b -[AvnWindow windowWillClose:] + 143
24  com.apple.CoreFoundation      	0x00007fff20788483 __CFNOTIFICATIONCENTER_IS_CALLING_OUT_TO_AN_OBSERVER__ + 12
25  com.apple.CoreFoundation      	0x00007fff20823ef9 ___CFXRegistrationPost_block_invoke + 49
26  com.apple.CoreFoundation      	0x00007fff20823e74 _CFXRegistrationPost + 496
27  com.apple.CoreFoundation      	0x00007fff2075970e _CFXNotificationPost + 736
28  com.apple.Foundation          	0x00007fff214cbbc8 -[NSNotificationCenter postNotificationName:object:userInfo:] + 59
29  com.apple.AppKit              	0x00007fff2384e71b -[NSWindow _finishClosingWindow] + 124
30  com.apple.AppKit              	0x00007fff232ddc80 -[NSWindow _close] + 347
31  libAvaloniaNative.dylib       	0x00000001059123d4 WindowBaseImpl::Close() + 102
32  libAvaloniaNative.dylib       	0x000000010591245c virtual thunk to WindowBaseImpl::Close() + 16