Build, install, and check json_view.hpp

The new single header goes through the same checks and install steps as
json.hpp and json_fwd.hpp:

- cmake/ci.cmake: ci_test_amalgamation regenerates, formats, and compares
  json_view.hpp as well
- check_amalgamation.yml: the pull request check does the same; it runs
  develop's tools, so it needs config_json_view.json on develop first
- meson.build: installs single_include/nlohmann/json_view.hpp
- gen_bazel_build_file.cmake, BUILD.bazel: json_view.hpp joins the
  single-header target; the glob of the other target already covers the
  new headers
- labeler.yml: an "aspect: json_view" label for the header, its
  detail/view headers, tests, and documentation

The CMake install rules for include/ and single_include/, the REUSE
catch-all, and Package.swift cover the new files without changes.

Signed-off-by: Niels Lohmann <mail@nlohmann.me>

.github/workflows/check_amalgamation.yml

@@ -67,12 +67,13 @@ jobs:
 
           python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json.json -s .
           python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json_fwd.json -s .
+          python3 $TOOL_DIR/amalgamate.py -c $TOOL_DIR/config_json_view.json -s .
 
           # the header list of the Bazel "json" target must match the files in include/
           cmake -P cmake/scripts/gen_bazel_build_file.cmake
 
           ${{ github.workspace }}/venv/bin/astyle --project=tools/astyle/.astylerc --suffix=none --quiet \
-            $INCLUDE_DIR/json.hpp $INCLUDE_DIR/json_fwd.hpp
+            $INCLUDE_DIR/json.hpp $INCLUDE_DIR/json_fwd.hpp $INCLUDE_DIR/json_view.hpp
 
           # fail loudly if a directory is renamed or removed: find would only warn
           # about the missing path and silently drop its files from the check