[textinput] mv to builtins dir as hard-coded builtin

[ferdymercury]

This Pull request:

Changes or fixes:

A standalone library that could be swapped in the future with another one, eg LLVM's LineEditor, does not make sense to lie inside the "Core" ROOT folder, it's kind of an outside dependency, not central to ROOT's core system.

This textinput library was thought as standalone library, and in fact has a separate license from ROOT. It has its own namespace, etc. Make that clearer by moving it to builtins dir as hard-coded builtin such as mathtext or libafterimage

This will make the granularity and modularity clearer eg for Debian package maintainers for a future migration eg for the license auditing. It would allow them to have it as separate package rather than a big monolithic libCore library. And one could consider later replacing it with llvm textinput or other drop in replacements, without having to touch ROOT core folder.

Makes clearer what is inside ROOT and what is an independent outside component that can be externalized or changed to other lib.

In a future modularization step, one could make this a full separate library (such as #16438) linked by core via target_link_libraries. Now is just a cosmetic / logic directory structure reorganization, such as with mathtext, etc.

Checklist:

• tested changes locally
• updated the docs (if necessary)

[github-actions]

Test Results

    23 files      23 suites   3d 14h 6m 3s ⏱️
 3 855 tests  3 854 ✅ 0 💤 1 ❌
79 476 runs  79 475 ✅ 0 💤 1 ❌

For more details on these failures, see this check.

Results for commit 4575fee.

♻️ This comment has been updated with latest results.

[ferdymercury]

Failures seem unrelated

[pcanal]

The error might be related as they are possibly indicative of an inconsistent build:

<<< cling interactive line includer >>>: fatal error: module file '/github/home/ROOT-CI/build/lib/std.pcm' is out of date and needs to be rebuilt: signature mismatch
dataframe_friends: /github/home/ROOT-CI/src/interpreter/llvm-project/clang/include/clang/Basic/SourceLocation.h:343: unsigned int clang::PresumedLoc::getLine() const: Assertion `isValid()' failed.
CMake Error at /github/home/ROOT-CI/src/cmake/modules/RootTestDriver.cmake:256 (message):
  error code: Subprocess aborted

[pcanal]

Restarting the build as 'clean build' to see if this is the case.

[ferdymercury]

Remaining failure is unrelated