completion/bash: add completion rules for ctags

[masatake]

Close #1168.

The changes for Makefile.am and configure.ac are derrived from util-linux. Their licenses are covered withn "The ./COPYING file (GPL-2.0-or-later)".

Quoted from README.licensing:

The project util-linux doesn't use the same license for all of the code.
There is code under:

   * GPL-3.0-or-later   - GNU General Public License version 3, or any later version

   * GPL-2.0-or-later   - GNU General Public License version 2, or any later version

   * GPL-2.0            - GNU General Public License version 2

   * LGPL-2.1-or-later  - GNU Lesser General Public License 2.1 or any later version

   * BSD-3-Clause       - BSD 3-Clause "New" or "Revised" License

   * BSD-4-Clause-UC    - BSD 4-Clause University of California-Specific

   * Public Domain

Please, check the source code for more details. A license is usually at the start
of each source file.

The ./COPYING file (GPL-2.0-or-later) is the default license for code without
an explicitly defined license.

---

TODO:

• revise
• Don't hard code column numbers when parsing --list-* output
• Pass --options=NONE --quiet when running ctags internally
• --roles-
• --param-
• --list-roles
• --list-subparsers
• the rules for readtags

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.40%. Comparing base (8334234) to head (70a8718).
⚠️ Report is 1943 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #3504   +/-   ##
=======================================
  Coverage   83.40%   83.40%           
=======================================
  Files         220      220           
  Lines       52970    52970           
=======================================
  Hits        44181    44181           
  Misses       8789     8789           

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