docs: kernel-doc: python: strip __counted_by_ptr macro

The `__counted_by_ptr` macro was recently introduced [1] to extend
bounds checking semantics to standard dynamically allocated pointers.

However, the new Python implementation of kernel-doc does not currently
recognize it as a compiler attribute. When kernel-doc encounters a
struct member annotated with this macro, it fails to parse the variable
name correctly, resulting in false-positive warnings like:

  Warning: ... struct member '__counted_by_ptr(cmdcnt' not described

Add `__counted_by_ptr` to the `struct_xforms` regex list so it gets
safely stripped out during the parsing phase, mirroring the existing
behavior for `__counted_by`. Update the corresponding unit tests.

Link: https://git.kernel.org/torvalds/c/150a04d817d8 [1]
Signed-off-by: Tudor Ambarus <tudor.ambarus@linaro.org>
Reviewed-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Reviewed-by: Kees Cook <kees@kernel.org>
Acked-by: Randy Dunlap <rdunlap@infradead.org>
Tested-by: Randy Dunlap <rdunlap@infradead.org>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20260506-kdoc-__counted_by_ptr-v1-1-70763486871f@linaro.org>

tools/lib/python/kdoc/xforms_lists.py

@@ -29,6 +29,7 @@ class CTransforms:
         (CMatch("__aligned"), ""),
         (CMatch("__counted_by"), ""),
         (CMatch("__counted_by_(le|be)"), ""),
+        (CMatch("__counted_by_ptr"), ""),
         (CMatch("__guarded_by"), ""),
         (CMatch("__pt_guarded_by"), ""),
         (CMatch("__packed"), ""),

tools/unittests/test_cmatch.py

@@ -320,6 +320,7 @@ class TestSubWithLocalXforms(TestCaseDiff):
         (CMatch('__aligned'), ' '),
         (CMatch('__counted_by'), ' '),
         (CMatch('__counted_by_(le|be)'), ' '),
+        (CMatch('__counted_by_ptr'), ' '),
         (CMatch('__guarded_by'), ' '),
         (CMatch('__pt_guarded_by'), ' '),