[OptTable] Support grouped short options

POSIX.1-2017 12.2 Utility Syntax Guidelines, Guideline 5 says:

> One or more options without option-arguments, followed by at most one option that takes an option-argument, should be accepted when grouped behind one '-' delimiter.

i.e. -abc represents -a -b -c. The grouped short options are very common.  Many
utilities extend the syntax by allowing (an option with an argument) following a
sequence of short options.

This patch adds the support to OptTable, similar to cl::Group for CommandLine
(D58711).  llvm-symbolizer will use the feature (D83530). CommandLine is exotic
in some aspects. OptTable is preferred if the user wants to get rid of the
behaviors.

* `cl::opt<bool> i(...)` can be disabled via -i=false or -i=0, which is
  different from conventional --no-i.
* Handling --foo & --no-foo requires a comparison of argument positions,
  which is a bit clumsy in user code.

OptTable::parseOneArg (non-const reference InputArgList) is added along with
ParseOneArg (const ArgList &). The duplicate does not look great at first
glance. However, The implementation can be simpler if ArgList is mutable.
(ParseOneArg is used by clang-cl (FlagsToInclude/FlagsToExclude) and lld COFF
(case-insensitive). Adding grouped short options can make the function even more
complex.)

The implementation allows a long option following a group of short options. We
probably should refine the code to disallow this in the future. Allowing this
seems benign for now.

Reviewed By: grimar, jhenderson

Differential Revision: https://reviews.llvm.org/D83639

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