Optimize generic collection Equal

[jnyrup]

This PR optimizes Equal for generic collections as #490 mentioned performance problems.
The slowdown was mostly due generic collections of value types being boxed.

A minor downside is that now the subject will now be enumerated twice when failing, whereas before it was a copy of the subject that got enumerated in EnumerableValueFormatter.
I believe this is worthwhile as we should optimize for tests passing.

In the benchmark:

• CollectionEqual_NonGeneric is equivalent to the current behavior,
• CollectionEqual_Generic is the optimized version from this PR.
• CollectionEqual_Generic_Equality is using a custom comparer in the benchmark, (int s, int e) => s == e in this example.

BenchmarkDotNet=v0.10.14, OS=Windows 10.0.16299.371 (1709/FallCreatorsUpdate/Redstone3)
Intel Core i7-6700HQ CPU 2.60GHz (Skylake), 1 CPU, 8 logical and 4 physical cores
Frequency=2531245 Hz, Resolution=395.0625 ns, Timer=TSC
  [Host]    : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 64bit RyuJIT-v4.7.2633.0
  RyuJitX86 : .NET Framework 4.7.1 (CLR 4.0.30319.42000), 32bit LegacyJIT-v4.7.2633.0

Job=RyuJitX86  Jit=RyuJit  Platform=X86

                                  Method |     N |         Mean |      Error |     StdDev | Scaled |    Gen 0 |   Gen 1 | Allocated |
---------------------------------------- |------ |-------------:|-----------:|-----------:|-------:|---------:|--------:|----------:|
              CollectionEqual_NonGeneric |    10 |     4.623 us |  0.0534 us |  0.0500 us |   1.00 |   0.6866 |       - |   2.12 KB |
                 CollectionEqual_Generic |    10 |     1.563 us |  0.0224 us |  0.0210 us |   0.34 |   0.5054 |       - |   1.56 KB |
 CollectionEqual_Generic_IsSameOrEqualTo |    10 |     1.586 us |  0.0174 us |  0.0162 us |   0.34 |   0.5436 |       - |   1.68 KB |
        CollectionEqual_Generic_Equality |    10 |     1.476 us |  0.0123 us |  0.0115 us |   0.32 |   0.4673 |       - |   1.44 KB |
                                         |       |              |            |            |        |          |         |           |
              CollectionEqual_NonGeneric |   100 |    26.771 us |  0.2284 us |  0.2137 us |   1.00 |   1.9531 |       - |   6.05 KB |
                 CollectionEqual_Generic |   100 |     2.945 us |  0.0351 us |  0.0328 us |   0.11 |   0.8469 |       - |   2.61 KB |
 CollectionEqual_Generic_IsSameOrEqualTo |   100 |     3.751 us |  0.0633 us |  0.0561 us |   0.14 |   1.2283 |       - |   3.79 KB |
        CollectionEqual_Generic_Equality |   100 |     2.501 us |  0.0391 us |  0.0366 us |   0.09 |   0.4654 |       - |   1.44 KB |
                                         |       |              |            |            |        |          |         |           |
              CollectionEqual_NonGeneric |  1000 |   242.738 us |  3.3402 us |  3.1244 us |   1.00 |  13.1836 |       - |  41.22 KB |
                 CollectionEqual_Generic |  1000 |    16.479 us |  0.2279 us |  0.2132 us |   0.07 |   4.2725 |       - |  13.16 KB |
 CollectionEqual_Generic_IsSameOrEqualTo |  1000 |    24.522 us |  0.2887 us |  0.2701 us |   0.10 |   8.0872 |       - |  24.88 KB |
        CollectionEqual_Generic_Equality |  1000 |    12.737 us |  0.1292 us |  0.1209 us |   0.05 |   0.4578 |       - |   1.44 KB |
                                         |       |              |            |            |        |          |         |           |
              CollectionEqual_NonGeneric |  5000 | 1,247.512 us | 14.8358 us | 13.1515 us |   1.00 |  74.2188 |  9.7656 | 247.05 KB |
                 CollectionEqual_Generic |  5000 |    76.284 us |  1.1535 us |  1.0790 us |   0.06 |  19.5313 |       - |  60.04 KB |
 CollectionEqual_Generic_IsSameOrEqualTo |  5000 |   116.489 us |  0.8728 us |  0.7737 us |   0.09 |  38.5742 |       - | 118.63 KB |
        CollectionEqual_Generic_Equality |  5000 |    57.726 us |  0.4890 us |  0.4574 us |   0.05 |   0.4272 |       - |   1.44 KB |
                                         |       |              |            |            |        |          |         |           |
              CollectionEqual_NonGeneric | 10000 | 2,511.052 us | 27.8286 us | 26.0309 us |   1.00 | 113.2813 | 39.0625 | 492.26 KB |
                 CollectionEqual_Generic | 10000 |   150.334 us |  2.0317 us |  1.9005 us |   0.06 |  38.5742 |       - | 118.63 KB |
 CollectionEqual_Generic_IsSameOrEqualTo | 10000 |   231.409 us |  1.7973 us |  1.6812 us |   0.09 |  76.6602 |       - | 235.82 KB |
        CollectionEqual_Generic_Equality | 10000 |   114.122 us |  1.0269 us |  0.8575 us |   0.05 |   0.3662 |       - |   1.44 KB |