list or execute code actions

Usage:
  gopls [flags] codeaction [codeaction-flags] filename[:line[:col]]


The codeaction command lists or executes code actions for the
specified file or range of a file. Each code action contains
either an edit to be directly applied to the file, or a command
to be executed by the server, which may have an effect such as:
- requesting that the client apply an edit;
- changing the state of the server; or
- requesting that the client open a document.

The -kind and and -title flags filter the list of actions.

The -kind flag specifies a comma-separated list of LSP CodeAction kinds.
Only actions of these kinds will be requested from the server.
Valid kinds include:

	gopls.doc.features
	quickfix
	refactor
	refactor.extract
	refactor.extract.constant
	refactor.extract.function
	refactor.extract.method
	refactor.extract.toNewFile
	refactor.extract.variable
	refactor.inline
	refactor.inline.call
	refactor.rewrite
	refactor.rewrite.changeQuote
	refactor.rewrite.fillStruct
	refactor.rewrite.fillSwitch
	refactor.rewrite.invertIf
	refactor.rewrite.joinLines
	refactor.rewrite.removeUnusedParam
	refactor.rewrite.splitLines
	source
	source.assembly
	source.doc
	source.fixAll
	source.freesymbols
	source.organizeImports
	source.test

Kinds are hierarchical, so "refactor" includes "refactor.inline".
(Note: actions of kind "source.test" are not returned unless explicitly
requested.)

The -title flag specifies a regular expression that must match the
action's title. (Ideally kinds would be specific enough that this
isn't necessary; we really need to subdivide refactor.rewrite; see
gopls/internal/settings/codeactionkind.go.)

The -exec flag causes the first matching code action to be executed.
Without the flag, the matching actions are merely listed.

It is not currently possible to execute more than one action,
as that requires a way to detect and resolve conflicts.
TODO(adonovan): support it when golang/go#67049 is resolved.

If executing an action causes the server to send a patch to the
client, the usual -write, -preserve, -diff, and -list flags govern how
the client deals with the patch.

Example: execute the first "quick fix" in the specified file and show the diff:

	$ gopls codeaction -kind=quickfix -exec -diff ./gopls/main.go

codeaction-flags:
  -d,-diff
    	display diffs instead of edited file content
  -exec
    	execute the first matching code action
  -kind=string
    	comma-separated list of code action kinds to filter
  -l,-list
    	display names of edited files
  -preserve
    	with -write, make copies of original files
  -title=string
    	regular expression to match title
  -w,-write
    	write edited content to source files