Improve on_build, on_build_file and on_xxx for target and rule

[waruqi]

Improve on_build in target/rule

We can call original build script:

on_build(function (target, opt)
    opt.origin(target, opt)
end)

Add before/after/on_build_file in target

before_build_file(function (target, sourcefile, opt)
end)

on_build_file(function (target, sourcefile, opt)
    opt.origin(target, sourcefile, opt)
end)

after_build_file(function (target, sourcefile, opt)
end)

Add before/after/on_build_files in target

before_build_files(function (target, sourcebatch, opt)
end)

on_build_files(function (target, sourcebatch, opt)
    opt.origin(target, sourcebatch, opt)
end)

before_build_files(function (target, sourcebatch, opt)
end)

[waruqi]

#261

[waruqi]

Documents: https://xmake.io/#/zh/manual?id=targeton_build_file