Fix bazel_to_cmake expand_template if parent directory does not exist

[LDeakin]

This fixes expand_template in bazel_to_cmake so that it creates the parent directory of the output if it does not exist.

This partially fixes a cmake-based build for me, which otherwise errors as below:

Traceback (most recent call last):
  File "/home/lachy/dev/tensorstore/tools/cmake/bazel_to_cmake/bzl_library/expand_template.py", line 50, in <module>
    main()
  File "/home/lachy/dev/tensorstore/tools/cmake/bazel_to_cmake/bzl_library/expand_template.py", line 44, in main
    expand_template(
  File "/home/lachy/dev/tensorstore/tools/cmake/bazel_to_cmake/bzl_library/expand_template.py", line 32, in expand_template
    pathlib.Path(out).write_text(text, encoding='utf-8')
  File "/usr/lib/python3.11/pathlib.py", line 1079, in write_text
    with self.open(mode='w', encoding=encoding, errors=errors, newline=newline) as f:
         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/pathlib.py", line 1045, in open
    return io.open(self, mode, buffering, encoding, errors, newline)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
FileNotFoundError: [Errno 2] No such file or directory: '/home/lachy/dev/tensorstore/build/_deps/nghttp2-build/lib/includes/nghttp2/nghttp2ver.h'

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[brian-michell]

I just wanted to chime in and say this fixed build issues with nghttp2 for me as well, and much nicer than the hack I have for testing on cloud.