Add custom command in vs project generator

[waruqi]

Related issues: #1735

[waruqi]

I have supported it only for rules with batchcmds

example: tests/project/other/bin2c

rule("foo")
    after_buildcmd(function (target, batchcmds, opt)
        batchcmds:show("hello xmake!")
        batchcmds:cp("xmake.lua", "/tmp/")
        -- batchcmds:execv("echo", {"hello", "world!"})
        -- batchcmds:runv("echo", {"hello", "world!"})
    end)

target("test")
    set_kind("binary")
    add_rules("foo")
    add_files("src/*.c")

xmake project -k vs