lib/fs/mkstemp/, src/: Move fmkomstemp() to separate files under lib/fs/mkstemp/, and split into mkomstemp()

[alejandro-colomar]

This reduces the complexity of fmkomstemp() by adding a helper API, and moves this into the lib/fs/ library subdir.

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Revisions:

v1b

• Rebase

$ git range-diff master..gh/fmkomstemp shadow/master..fmkomstemp 
1:  257e2aaf = 1:  aa3d3676 lib/fs/mkstemp/, src/: fmkomstemp(): Move function to separate file
2:  6b28ca78 = 2:  dae656e6 lib/fs/mkstemp/: mkostemp(): Split API from fmkomstemp()

v1c

• Rebase

$ git range-diff master..gh/fmkomstemp shadow/master..fmkomstemp 
1:  aa3d3676 = 1:  3dfeb6fe lib/fs/mkstemp/, src/: fmkomstemp(): Move function to separate file
2:  dae656e6 = 2:  f6224cb4 lib/fs/mkstemp/: mkostemp(): Split API from fmkomstemp()

v1d

• Rebase

$ git range-diff master..gh/fmkomstemp shadow/master..fmkomstemp 
1:  3dfeb6fe = 1:  bf5be95a lib/fs/mkstemp/, src/: fmkomstemp(): Move function to separate file
2:  f6224cb4 = 2:  3e913b68 lib/fs/mkstemp/: mkostemp(): Split API from fmkomstemp()

[alejandro-colomar]

Queued after the release of 4.17.0.