Improve DefaultHttpXxx default paths

[benaadams]

• Reduce the number of (non-inlining) calls via interface to features get_Version
• Set up IHttpRequestFeature and IHttpResponseFeature while creating the context

Additionally there are compromises in DefaultHttpXxx for pooling; however this can be achieved without these compromises as well as improving the call chains to support devirtualization https://github.com/dotnet/coreclr/issues/9908.

• Implement PooledHttpContext though DefaultHttpContext rather than via inheritance.
• seal DefaultHttpXxx types to support devirtualization of overriden methods
• make DefaultHttpXxx private members direct types rather than parent types to support devirtualization
• Remove and don't call virtual methods from DefaultHttpXxx .ctors
• Make virtual methods in DefaultHttpXxx non-virtual

Non-DefaultHttpXxx can still be archived by inheriting from HttpXxx and either implementing via wrapping DefaultHttpXxx as per the Pooling example to make use of the feature caches; or by doing something alternative and using a completely different implementation.

[benaadams]

ApiCheck issues

[benaadams]

Related to call costs #811

[benaadams]

Before

                   Method |        Mean |    StdDev |         Op/s | Allocated |
------------------------- |------------ |---------- |------------- |---------- |
            CreateContext | 143.4606 ns | 0.9601 ns |   6970556.99 |     296 B |
           DisposeContext |   4.6421 ns | 0.0318 ns | 215420903.55 |       0 B |
              GetResponse |   3.3653 ns | 0.0784 ns | 297146866.37 |       0 B |
    GetResponseBodyCached |  11.0266 ns | 0.0513 ns |  90689729.30 |       0 B |
  GetResponseBodyUncached |  79.8499 ns | 0.3087 ns |  12523500.05 |       0 B |
   GetContentLengthCached |  31.3262 ns | 0.1729 ns |  31922152.25 |       0 B |
 GetContentLengthUncached | 103.7163 ns | 0.6423 ns |   9641681.62 |       0 B |

After

                   Method |        Mean |    StdDev |         Op/s | Allocated |
------------------------- |------------ |---------- |------------- |---------- |
            CreateContext | 143.7290 ns | 1.4642 ns |   6957536.80 |     296 B |
           DisposeContext |   4.3784 ns | 0.0212 ns | 228396085.62 |       0 B |
              GetResponse |   3.5320 ns | 0.0270 ns | 283129295.33 |       0 B |
    GetResponseBodyCached |  11.6523 ns | 0.0518 ns |  85819695.93 |       0 B |
  GetResponseBodyUncached |  64.5821 ns | 0.4103 ns |  15484163.61 |       0 B |
   GetContentLengthCached |  30.4709 ns | 0.2116 ns |  32818250.53 |       0 B |
 GetContentLengthUncached |  87.3118 ns | 0.7927 ns |  11453201.08 |       0 B |

Affects the uncached calls; didn't seem to really improve general call chain otherwise 😢

May need yet to be implmented devirualization/inlines

[benaadams]

Think also need to cut down on the amplification of (non-inlining) calls via interface to get_Version

1,002,263 calls for 143,180 plaintext requests

[benaadams]

Halved number of calls to revision

[davidfowl]

I would commit these separately.

[benaadams]

Removed

[benaadams]

Sorta; will get rid of the extras

[benaadams]

UpdateFeatures_ClearsCachedFeatures is a crazy test :-/

[muratg]

@benaadams is this an experimentation or a WIP for an actual change? :)

[benaadams]

Was an actual change; let me work out what it was doing again...

[benaadams]

I'll close and reopen :D