Use installed pybind11 and other CMake fixes

[jfpanisset]

• Adds OTIO_FIND_PYBIND11 configuration option to tell CMake to look for a pre-installed pybind11 instead of using the vendored copy. Follows existing pattern for Imath and rapidjson dependencies.
  Fixes #2006.

• Bugfixes in src/deps/CMakeLists.txt

  • checking for empty submodule directories was broken
  • Imath submodule would not get checked for emptiness
  • pybind11 dependency only required when building Python bindings

• Generated CMake files now installed in lib/cmake/opentime and lib/cmake/opentimelineio
  instead ofshare/opentime and share/opentimelineio as per CMake documentation.
  Fixes #2008.

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: jfpanisset / name: Jean-Francois Panisset (13b968c, 7925d57, d756ce9, da52ec1, dddc02d, fe051ac)

[jfpanisset]

Hmm, wasn't expecting this to break the build so badly. Converted PR to draft, looking into it.

[jfpanisset]

For this failed build:

https://github.com/AcademySoftwareFoundation/OpenTimelineIO/actions/runs/23814704627/job/69410968153?pr=2009

the error is:

CMake Error at src/deps/rapidjson/example/CMakeLists.txt:1 (cmake_minimum_required):
  Compatibility with CMake < 3.5 has been removed from CMake.

  Update the VERSION argument <min> value.  Or, use the <min>...<max> syntax
  to tell CMake that the project requires at least <min> but has been updated
  to work with policies introduced by <max> or earlier.

  Or, add -DCMAKE_POLICY_VERSION_MINIMUM=3.5 to try configuring anyway.

The src/deps/rapidjson submodule was updated to the latest commit, 24b5e7a and in example/CMakeLists.txt I find:

cmake_minimum_required(VERSION 2.8)

I see that my changes are actually trying to build the rapidjson submodule, but since it's a header only library, it doesn't need to get built, opentimelineio just needs to find the headers.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.14%. Comparing base (267fe4b) to head (da52ec1).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2009   +/-   ##
=======================================
  Coverage   85.14%   85.14%           
=======================================
  Files         181      181           
  Lines       12780    12780           
  Branches     1206     1206           
=======================================
  Hits        10882    10882           
  Misses       1715     1715           
  Partials      183      183           

Flag	Coverage Δ
py-unittests	85.14% <ø> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

---

Continue to review full report in Codecov by Sentry.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 267fe4b...da52ec1. Read the comment docs.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.