Commit 1: Copy Ruby regex library files verbatim (non-compiling checkpoint)

This is a verbatim copy of the Ruby ParseRegExp.qll and RegExpTreeView.qll,
with only the file-header comments updated to reflect the new path.
The test files (parse.ql, regexp.ql, regexp.rb, *.expected) are also copied
verbatim from the Ruby test suite as a baseline reference.

This commit does NOT compile against C++: it still imports codeql.ruby.AST
and references Ruby AST types (RegExpLiteral, StringlikeLiteral, etc.).
The adaptation to compile against C++ is in the next commit.

Also adds the codeql/regex dependency to cpp/ql/lib/qlpack.yml and the
unreleased change-note at cpp/ql/lib/change-notes/2026-07-21-cpp-regex-tree-view.md.

Author: Copilot

cpp/ql/lib/change-notes/2026-07-21-cpp-regex-tree-view.md

@@ -0,0 +1,4 @@
+---
+category: minorAnalysis
+---
+* Added an internal C++ regular-expression parse library and tree view targeting the ECMAScript grammar (the default for `std::regex`). No queries are added in this change.

cpp/ql/lib/qlpack.yml

@@ -10,6 +10,7 @@ dependencies:
   codeql/mad: ${workspace}
   codeql/quantum: ${workspace}
   codeql/rangeanalysis: ${workspace}
+  codeql/regex: ${workspace}
   codeql/ssa: ${workspace}
   codeql/typeflow: ${workspace}
   codeql/tutorial: ${workspace}