and simplify the implementation of the algorithm which reduces the number of ranges.

Previous fix was cloning the gROOT object rather than the user object (and
in practice was leading to an infinite recursion).  This corrects 3317c202.

This is required, for example, when building roottest externally
to find and run hsimple.C with root to generate hsimple.root.

ROOT-9956 #close

ROOT-9925 #close

- Modify original order of the vector elements

It is essential to keep the notion of non-relocatable headers, passed to
ROOT_GENERATE_DICTIONARY with full paths. The dictionary will remember them
with their original location, making sure that headers can be found at
runtime without -I or $ROOT_INCLUDE_PATH.

ROOT's headers will never be passed as full path; users as well as ROOT
itself (in contrast to the non-relocatable roottest) MUST pass relative
paths, as if they were to #include the header, together with a matching -I.

This can happen if the header is in an otehrwise excluded directory.
While we do not want to remember the -I in the PCH, we do want to
find the header to be injected into the dictionary!

This does not need an extra shared library, that needs to be searched and found.
Prevents extra gymnastics with finding the header at runtime.

Some of the tests need to find headers at runtime. Previously, these headers
were found by their full path; now, ROOT_GENERATE_DICTIONARY prefers relative
paths, that make dictionaries relocatable.
To not force everyone to define ROOT_INCLUDE_PATH when running e.g. a stress
test, the binaries call TROOT::AddExtraInterpreterArgs() passing the location
of the header, at runtime, such that cling can find them.

This is possible because the interpreter is constructed lazily, not during
static init; providing the extra interpreter flags early in main() is thus
sufficient.

This allows CMake to track the dependencies of G__Core vs headers.
It also simplifies the CMake code, e.g. by rendering the order of add_subdirectory(base) vs rest irrelevant.
It makes base, cont and other siblings symmetrical.

Enforce that headers *are* found, also by CMake, to ensure proper dependencies.
Add a backdoor for "you will not find the header": list those as GENHEADERS.
Add documentation, esp that headers should be passed to ROOT_GENERATE_DICTIONARY *as included*.
Use the directory (future: lib target) property for include directories.
Use these properties to pull in inc/ and v7/inc within ROOT_STANDARD_LIBRARY_PACKAGE, instead of hard-coded searches in ROOT_GENERATE_DICTIONARY.

This code must be replaced by a HeaderSearch of vector, stdio.h and then
use their DirectoryEntry-s as path for buildModuleMapOverlayEntry().

TClassEdit.h is a namespace in libCore and in the PCH.
There is no advantage in creating a dictionary for it.

We do not need dictionaries for internal Getline() functions or enums.

we don't care about enums that end up in the PCH anyway.

This makes the list of source files show up in one place instead of two.