Improve error/warning handling for invalid package configs and build targets

[Willaaaaaaa]

Is your feature request related to a problem? Please describe.

add_rules("mode.debug", "mode.release")

add_requires("ncnn[bulabula]")

target("test")
    add_files("*.cpp")
    add_packages("ncnn")

run xmake will successfully build the target with no error and warning message. But bulabula is an invalid config for ncnn package description. Hopefully, when a config is wrongly added, something like a warning/error is given.

And the same checks are hoped to be added in relevant apis like add_requireconfs().

Describe the solution you'd like

print a warning or raise an error. And although this can be a language server feature, I think we'd better provide a more strict and detailed check info for users.

-- something like this:
wprint("package(xxx): a, b, c configs are ignored, plz check the package description to determine which config(s) you should use")

[Willaaaaaaa]

A relevant bug

Problem

And the same for xmake build <target> command. When building an invalid target, xmake won't give any warning/error.

Current Behavior

$ xmake build tests  # build any invalid targets
[100%]: build ok, spent 0.007s

Expected behavior:

An invalid target shouldn't be "built ok".
Like xmake run <target>, tell users "error: 'xxxx' is not a valid target name for this project."