They affect all targets and make it more difficult to control the order
of the includes at a later stage.
Refs #0

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# especially if it merges an updated upstream into a topic branch.
#
# Lines starting with '#' will be ignored, and an empty message aborts
# the commit.

This reverts commit 480f7776.

Issues on clang:
07:12:15 Undefined symbols for architecture x86_64:
07:12:15   "Mantid::Types::Core::DateAndTime::MAX_NANOSECONDS",
referenced from:
07:12:15       Mantid::Types::Core::DateAndTime::maximum() in
DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::minimum() in
DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::operator-(long long)
const in DateAndTime.cpp.o
07:12:15
Mantid::Types::Core::DateAndTime::operator+(boost::posix_time::time_duration
const&) const in DateAndTime.cpp.o
07:12:15
Mantid::Types::Core::DateAndTime::operator-(boost::posix_time::time_duration
const&) const in DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::operator-(double) const
in DateAndTime.cpp.o
07:12:15   "Mantid::Types::Core::DateAndTime::MIN_NANOSECONDS",
referenced from:
07:12:15       Mantid::Types::Core::DateAndTime::maximum() in
DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::minimum() in
DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::operator-(long long)
const in DateAndTime.cpp.o
07:12:15
Mantid::Types::Core::DateAndTime::operator+(boost::posix_time::time_duration
const&) const in DateAndTime.cpp.o
07:12:15
Mantid::Types::Core::DateAndTime::operator-(boost::posix_time::time_duration
const&) const in DateAndTime.cpp.o
07:12:15       Mantid::Types::Core::DateAndTime::operator-(double) const
in DateAndTime.cpp.o
07:12:15 ld: symbol(s) not found for architecture x86_64
07:12:15 clang: error: linker command failed with exit code 1 (use -v to
see invocation)

Merge to ensure CrystalFieldFunction is available and up to date.

* Make Core::DateAndTimeHelpers::stringIsISO8601() to check for basic
ISO8601 strings as well.
* Add  stringIsPosix() method to DateAndTimeHelpers to check validity of
posix strings.
* Extend corresponding unit tests.
* Add the posix string check to DateAndTime::setFromISO8601().

Re #20969

Re #20969

Re #20969

Makes the function accessible to Types::Core::DateAndTime. The function
was originally using Poco which is not linked to Types. We now use
boost::regex instead.

Re #20969

CMake files updated to use the Types module

This step was taken to avoid introducing unnecesary inter=module
dependencies between Indexing and Beamline.