* Optimize (m ModuleInstance) String()
Optimize (m ModuleInstance) String() to preallocate the buffer and use strings.Builder instead of bytes.Buffer
This leads to a common case only doing a single allocation as opposed to a few allocations which the bytes.Buffer is doing.
* adding a benchmark test
Result:
```
$ go test -bench=String ./addrs -benchmem
BenchmarkStringShort-12 18271692 56.52 ns/op 16 B/op 1 allocs/op
BenchmarkStringLong-12 8057071 158.5 ns/op 96 B/op 1 allocs/op
PASS
$ git checkout main addrs/module_instance.go
$ go test -bench=String ./addrs -benchmem
BenchmarkStringShort-12 7690818 162.0 ns/op 80 B/op 2 allocs/op
BenchmarkStringLong-12 2922117 414.1 ns/op 288 B/op 3 allocs/op
```
* Update module_instance_test.go
switch spaces to tabs
Generating strings and comparing them to implement Equal is a quick and
easy solution. Unfortunately when this code is in the hot path, it
becomes very expensive, so this commit changes some of those instances
to compare the values directly.
Combined with using addr.Equal instead of checking for string equality,
this makes Terraform dramatically faster for some operations, such as
generating large JSON plans.
Dennis Gursky