Support merge_staticlib for static kind package

[star-hengxing]

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

A new policy, package.merge_staticlib, can be used for libraries like abseil that have many sub-libraries(86+), let xmake merge into a single static library.

Describe the solution you'd like

N/A

Describe alternatives you've considered

No response

Additional context

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[waruqi]

大概实现了，#5927

不过 .pc/.cmake 的导入文件没法处理，库名换了，可能会影响其他库去 find package，像 abeils 这种，一堆的 .pc ，不太适用

[star-hengxing]

不过 .pc/.cmake 的导入文件没法处理，库名换了，可能会影响其他库去 find package，像 abeils 这种，一堆的 .pc ，不太适用

没问题，这个功能就是方便用户而不是打包

[Issues-translate-bot]

Bot detected the issue body's language is not English, translate it automatically.

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However, the import file of .pc/.cmake cannot be processed. If the library name is changed, it may affect other libraries to find packages. A bunch of .pc files like abeils are not suitable.

No problem, this function is to facilitate users rather than packaging