feature request: refactor to expand and collapse expressions

It would be nice to be able to pull out repeated expressions or expand an expression on demand.
So one could jump back and forth between for example:

function love.draw()
    local w, h = love.graphics.getDimensions()
    love.graphics.setColor(1, 0, 0)
    love.graphics.circle('fill', 50, 50, 22)
    love.graphics.setColor(1, 1, 0)
    love.graphics.circle('fill', 50, 100, 22)
    love.graphics.setColor(0, 1, 0)
    love.graphics.circle('fill', 50, 150, 22)
end

and

local g = love.graphics

function love.draw()
    local w, h = g.getDimensions()
    g.setColor(1, 0, 0)
    g.circle('fill', 50, 50, 22)
    g.setColor(1, 1, 0)
    g.circle('fill', 50, 100, 22)
    g.setColor(0, 1, 0)
    g.circle('fill', 50, 150, 22)
end

It would also be nice to do this for local variables, so that the change is only applied where all the nessecary variables are visible (i.e. for required modules within a scope or long paths in arguments), so one can easily switch between

local function compileInfo(project)
    return {
        root = project.main,
        compiler = project.conf.toolchain == 'gnu' and 'gcc'
            or project.conf.toolchain == 'windows' and 'msvc'
            or project.conf.toolchain == 'clang' and 'clang'
    }
end

and

local function compileInfo(project)
    local c = project.conf
    return {
        root = project.main,
        compiler = c.toolchain == 'gnu' and 'gcc'
            or c.toolchain == 'windows' and 'msvc'
            or c.toolchain == 'clang' and 'clang'
    }
end

or

local function compileInfo(project)
    local t = project.conf.toolchain
    return {
        root = project.main,
        compiler = t == 'gnu' and 'gcc'
            or t == 'windows' and 'msvc'
            or t == 'clang' and 'clang'
	}
end

This is most usefull for long namespaced paths, but it may also be usefull to extract out some repeated constants or function calls and expand them again, so one can switch between:

local function copy(src, dst)
    for f in lfs.dir(src) do
        local src = io.open(src..package.config:sub(1, 1)..f, "rb")
        local dst = io.open(dst..package.config:sub(1, 1)..f, "wb")
    end
end

and

local DIR_SEP = package.config:sub(1, 1)

local function copy(src, dst)
    for f in lfs.dir(src) do
        local src = io.open(src..DIR_SEP..f, "rb")
        local dst = io.open(dst..DIR_SEP..f, "wb")
    end
end

Ideally one could chose the name of the pulled out expression via an prompt.

It's a long time since I had a good look at your codebase, so I wouldn't know where to start if I wanted to implement such a feature myself. I might be willing to try, if someone gives me a few pointers though.

该 issue 未指明文件、测试或入口点。首先梳理 language server 的重构或 code-action 实现，并确定应如何规定和测试作用域分析、命名提示、展开以及可撤销的变换。