docs: Update the api doc generation.

[prmukherj]

1. Improve code structure to improve API Reference.
2. Particular improvement in the meshing docs, to explain workflows, cross-referencing user guides examples, etc.

This is part of an incremental improvement task and following PRs will improve the docs further.

The current view of the API Reference:

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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