Port #39096 - Implementation of CSE for large constants on ARM64

[briansull]

• Implementation of code size optimization, CSE of large constants for ARM64

Implementation of code size optimization, CSE of large constant for ARM64
We will share a single CSE for constants that differ only in their low 12 bits on ARM64

Config variable: COMPlus_JitConstCSE
// Default 0: enable the CSE of Constants, including nearby offsets. (only for ARM64)
// If 1, disable all the CSE of Constants
// If 2, enable the CSE of Constants but don't combine with nearby offsets. (only for ARM64)
// If 3, enable the CSE of Constants including nearby offsets. (all platforms)
// If 4, enable the CSE of Constants but don't combine with nearby offsets. (all platforms)
//

• Change the type of csdHashKey to size_t
• Update gtCostSz and gtCostEx for constant nodes
• Added additional Priority 0 test coverage for Floating Point optimizations

[briansull]

I believe that the test failure is due to: #39473

runtime (Build Browser wasm Release AllSubsets_Mono) Failing after 74m — Build Browser wasm Release AllSubsets_Mono failed

This is what I found in the console log for the test leg:
https://helix.dot.net/api/2019-06-17/jobs/8ee35f01-bc0c-48a1-bd50-7a4e28e0dfa5/workitems/System.Formats.Asn1.Tests/console

[03:36:03] dbug: test[0]
      [FAIL] System.Formats.Asn1.Tests.Writer.WriteOctetString.WriteSegmentedCER
      System.NullReferenceException : Object reference not set to an instance of an object.
         at System.Reflection.CustomAttributeTypedArgument.CanonicalizeValue(Object value)
         at System.Reflection.CustomAttributeTypedArgument..ctor(Type argumentType, Object value)
         at System.Reflection.CustomAttributeData.ResolveArguments()
         at System.Reflection.CustomAttributeData.get_ConstructorArguments()
         at ReflectionAbstractionExtensions.GetCustomAttributes(IMethodInfo methodInfo, Type attributeType)

[briansull]

@jeffschwMSFT PTAL

[briansull]

@BruceForstall @sandreenko @erozenfeld PTAL