[Test Framework] Add initial support for Matchers

[SupunS]

Work towards https://github.com/onflow/cadence/issues/331

Description

Supports:

• Equal matcher

  // matcher with primitive type
  let matcher = Test.equal(1)
  
  // matcher with struct type
  let matcher = Test.equal(Foo())
  
  // matcher with resource type
  let f <- create Foo()
  let matcher = Test.equal(<-f)
  

• Custom matchers: Supports defining custom matchers that deal with AnyStruct type.

  e.g.(1): Customer matcher for a primitive type

  let matcher = Test.NewMatcher(fun (_ value: Int): Bool {
      return value == 7
  })
  
  assert(matcher.test(7))
  

  e.g.(2): Customer matcher for a struct type

  let matcher = Test.NewMatcher(fun (_ value: AnyStruct): Bool {
      if !value.isInstance(Type<Int>()) {
          return false
      }
  
      return (value as! Int) > 5
  })
  
  assert(matcher.test(8))
  

  e.g.(3): Customer matcher for handling resource type. Even though resource types are not supported, it can be made to work with a resource reference

  let matcher = Test.NewMatcher(fun (_ value: &Foo): Bool {
      return value.a == 4
  })
  
  let f <-create Foo(4)
  assert(matcher.test(&f as &Foo))
  

• Expect function

  let matcher = Test.equal("other string")
  Test.expect("this string", matcher)
  

  *This API was slightly changed compared to the proposal, to support resources. This API is not final and can be adjusted based on requirements/feedback.

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• [ ] Targeted PR against master branch
• [x] Linked to Github issue with discussion and accepted design OR link to spec that describes this work
• [x] Code follows the standards mentioned here
• [x] Updated relevant documentation
• [x] Re-reviewed Files changed in the Github PR explorer
• [x] Added appropriate labels