Problem:  filetype: some requirements files are not recognized
Solution: Detect '*-requirements.txt', 'constraints.txt',
          'requirements.in', 'requirements/*.txt' and 'requires/*.txt'
          as requirements filetype, include pip compiler, include
          requirements filetype and syntax plugin
          (Wu, Zhenyu, @raimon49)

closes: vim/vim#14379

https://github.com/vim/vim/commit/f9f5424d3e75bbdb35aa48fa6f9241d9479b35e8

Co-authored-by: Wu, Zhenyu <wuzhenyu@ustc.edu>
Co-authored-by: raimon <raimon49@hotmail.com>