[script] add script to check, enforce, and update header guards (#12227)

This commit introduces a new script `update-header-guards.py` which
checks for the presence of header guards in `.h` and `.hpp` files and
automatically updates them, standardizing the header guard name format
across the codebase.

The new format for header guards is derived from the full path of the
file. For example, `src/core/common/notifier.hpp` will use
`OT_CORE_COMMON_NOTIFIER_HPP_`. The guard name includes additional
prefixes such as `OT_` or `OPENTHREAD_` to ensure uniqueness.

This new naming format handles cases where the same filename may be used
in different folders, such as the two `heap.hpp` files located in
`src/core/common` and `src/core/utils`.

It also ensures that public and platform OpenThread headers under
`include/openthread` have uniquely distinct header guard names to avoid
conflicts when these headers are included in other projects.

The new script helped identify issues with existing header files that
lacked header guards (e.g., `posix/system.hpp`) or had improper guards
(e.g., `openthread/link_metrics.h`).

This commit also introduces a new check script `check-header-guards` to
validate that all header guards are correctly formatted. This check is
added to the GitHub CI actions to ensure consistency moving forward.

All existing header files have been updated (using the new script)
to apply the new guard name format.

.github/workflows/makefile-check.yml

@@ -58,3 +58,16 @@ jobs:
     - name: Check
       run: |
         script/check-core-makefiles
+
+  header-guard-check:
+    runs-on: ubuntu-24.04
+    steps:
+    - name: Harden Runner
+      uses: step-security/harden-runner@f4a75cfd619ee5ce8d5b864b0d183aff3c69b55a # v2.13.1
+      with:
+        egress-policy: audit # TODO: change to 'egress-policy: block' after couple of runs
+
+    - uses: actions/checkout@08c6903cd8c0fde910a37f88322edcfb5dd907a8 # v5.0.0
+    - name: Check
+      run: |
+        script/check-header-guards