Redundant global read

In situations when global reads immediately after write we could avoid this read and use argument of global.set. For example this:

(module
  (global $g (mut i32) (i32.const 0))
  (func $test (param $0 i32) (result i32)
    (global.set $g (local.get $0))
    (global.get $g)
  )
)

can be optimized as:

(module
  (global $g (mut i32) (i32.const 0))
  (func $test (param $0 i32) (result i32)
    (global.set $g (local.get $0))
    (local.get $0)
  )
)

if arg is simple like local.get or i32.const
and something like this if arg more complex:

(module
  (global $g (mut i32) (i32.const 0))
  (func $test (param $0 i32) (result i32)
    (global.set $g (local.tee $tmp (...complex expr...)))
    (local.get $tmp)
  )
)

Start by locating Binaryen's optimization pass that handles global.set and global.get, then inspect existing tests for global transformations. Add coverage for simple and complex values as shown in the issue, and consider the work done when the redundant read is removed while the examples retain their behavior.