Standardize diffuse irradiance component names and descriptions in docstrings

[cbcrespo]

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As pointed out by @cwhanse here, there were previously some discrepancies between the docstring names and definitions of different diffuse irradiance components between different functions. This PR aims to standardize those names and definitions.

Some functions were not addressed in this PR as they were already addressed in their own PRs:

• isotropic: Add support for return_components to irradiance.isotropic #2787
• reindl: Add support for return_components to Reindl #2775
• get_sky_diffuse, poa_components, and get_total_irradiance: Add diffuse components support: get_sky_diffuse, poa_components, and get_total_irradiance #2800