[sgen] Add major concurrent collector stw time to "Major GC time" counter
[sgen] Add concurrent collector counter for time spent during concurrent phase
[sgen] Don't get time twice at the same time.
Test Rss20ItemFormatter.ReadFrom Guid. Covers 23262.
Rss20ItemFormatter.ReadFrom now sets Id when guid is PermaLink.
Fixes 23262.
Merge pull request #1307 from esdrubal/servicemodelrss

Rss20ItemFormatter.ReadFrom now sets Id when guid is PermaLink.
Test Json deserialization of a floating-point number as object.
Covers 21583.
Improved Json deserialization of floating-point numbers.
When DataContractJsonSerializer was created from type object, deserialization of floating.point numbers was not possible.
Fixes 21583.
Merge pull request #1309 from esdrubal/json

Improved Json deserialization of floating-point numbers.
[runtime] Implement lazy resolution of array interfaces.

To resolve casting we make all relevant interfaces to use the generic variance casting code.
This only affected ICollection`1 and IList`1, which are not terribly popular.

To fix dispatch we augment vtable resolution to treat those interfaces as variant and use
the already in place machinery.

Memory reduction numbers for the corlib test suite:

Initialized classes 8004 -> 7470 (7% reduction)
Corlib mempool size: 2719832 -> 2678872 (1.5% reduction)

Inflated classes 4500: 3.972 (12% reduction)
Inflated signatures size: 166128 -> 139812 (16% reduction)
Inflated methods size: 565152 -> 485664 (15$ reduction)
[runtime] Remove a bit chunk of what's dead code now.