Remove generics from IAvaloniaObject.

[grokys]

What does the pull request do?

We have a problem with our usage of generic virtual and generic interface methods, in that they cause performance problems in the JIT. We've decided that for 11.0 we need to at least remove generic interface methods from the public API. This PR removes generic methods from the IAvaloniaObject interface.

In order to do so, I had to throw exceptions in quite a few places if the IAvaloniaObject instance isn't an AvaloniaObject. Reimplementing this interface wasn't really feasible anyway so this shouldn't cause a problem in practise (and in future we will probably want to remove this interface completely but baby steps for now).

Breaking Changes

Yes :P

[workgroupengineering]

For curiosity. How much does performance improve?

[grokys]

I doubt that it's changed much from just this PR - there are a couple of other more impactful changes that I'm about to make, and I'll benchmark once those are done. Wanted to separate the PRs though for easier review.

[grokys]

A quick preview of a few selected benchmarks after this and some other changes:

master

|                             Method |       Mean |     Error |    StdDev | Ratio | RatioSD |   Gen 0 | Allocated |
|----------------------------------- |-----------:|----------:|----------:|------:|--------:|--------:|----------:|
|               SetClrPropertyValues |   5.069 us | 0.0237 us | 0.0222 us |  1.00 |    0.00 |       - |         - |
|                          SetValues | 164.066 us | 0.8528 us | 0.7560 us | 32.36 |    0.18 | 41.9922 |  88,000 B |
| Set_Local_Values_With_Style_Values | 253.437 us | 1.6218 us | 1.3542 us | 49.97 |    0.43 | 80.0781 | 168,001 B |

|                                     Method |     Mean |   Error |  StdDev |    Gen 0 | Allocated |
|------------------------------------------- |---------:|--------:|--------:|---------:|----------:|
|          Setup_Dispose_LocalValue_Bindings | 380.7 us | 1.85 us | 1.64 us | 215.8203 |    441 KB |
|                   Fire_LocalValue_Bindings | 135.6 us | 0.82 us | 0.73 us |  45.4102 |     93 KB |
| Fire_LocalValue_Bindings_With_Style_Values | 253.5 us | 1.86 us | 1.55 us |  86.9141 |    178 KB |

|         Method |        Mean |       Error |      StdDev |      Median |   Gen 0 |   Gen 1 | Allocated |
|--------------- |------------:|------------:|------------:|------------:|--------:|--------:|----------:|
| CreateCalendar | 27,451.2 us | 2,055.70 us | 5,898.20 us | 24,671.8 us |       - |       - |  4,356 KB |
|   CreateButton |    206.3 us |     0.88 us |     0.78 us |    206.3 us | 20.7520 |  0.4883 |     43 KB |
|  CreateTextBox |  1,355.8 us |     7.59 us |     6.73 us |  1,357.6 us | 78.1250 | 23.4375 |    225 KB |

after refactoring

|                             Method |       Mean |     Error |    StdDev | Ratio | RatioSD |   Gen 0 | Allocated |
|----------------------------------- |-----------:|----------:|----------:|------:|--------:|--------:|----------:|
|               SetClrPropertyValues |   5.018 us | 0.0084 us | 0.0070 us |  1.00 |    0.00 |       - |         - |
|                          SetValues | 134.237 us | 0.6255 us | 0.5545 us | 26.75 |    0.12 | 41.9922 |  88,000 B |
| Set_Local_Values_With_Style_Values | 217.688 us | 1.2422 us | 1.1619 us | 43.35 |    0.26 | 80.3223 | 168,000 B |

|                                     Method |     Mean |   Error |  StdDev |    Gen 0 | Allocated |
|------------------------------------------- |---------:|--------:|--------:|---------:|----------:|
|          Setup_Dispose_LocalValue_Bindings | 310.6 us | 2.15 us | 1.79 us | 219.2383 |    448 KB |
|                   Fire_LocalValue_Bindings | 107.3 us | 0.76 us | 0.68 us |  45.6543 |     93 KB |
| Fire_LocalValue_Bindings_With_Style_Values | 199.0 us | 1.00 us | 0.94 us |  87.1582 |    178 KB |

|         Method |        Mean |       Error |      StdDev |      Median |   Gen 0 |   Gen 1 | Allocated |
|--------------- |------------:|------------:|------------:|------------:|--------:|--------:|----------:|
| CreateCalendar | 25,469.2 us | 2,107.63 us | 6,081.00 us | 22,432.5 us |       - |       - |  4,365 KB |
|   CreateButton |    190.1 us |     0.90 us |     0.85 us |    189.8 us | 20.5078 |  0.2441 |     42 KB |
|  CreateTextBox |  1,284.4 us |    10.76 us |    10.06 us |  1,283.2 us | 76.1719 | 21.4844 |    225 KB |

So looks like we're seeing a 10-20% speedup in some benchmarks.

[grokys]

Full benchmarks after the first batch of changes at #7980

[grokys]

Closing this as I think #7980 should be the one we merge (which includes this and #7979).