rename selected identifier

Usage:
  gopls [flags] rename [rename-flags] <position> <name>

Example:

	$ # 1-based location (:line:column or :#position) of the thing to change
	$ gopls rename helper/helper.go:8:6 Foo
	$ gopls rename helper/helper.go:#53 Foo

rename-flags:
  -d,-diff
    	display diffs instead of rewriting files
  -preserve
    	preserve original files
  -w,-write
    	write result to (source) file instead of stdout
