[Documentation] Updated Categorical Focal Crossentropy Loss Docstring

[samitshah1]

What's the update?

• Updated example in docstring for Categorical Focal Crossentropy Loss
• Fixed typos in docstring for Binary Focal Crossentropy Loss

Why was the update required?

• While reading the documentation for Categorical Focal Crossentropy Loss, the example imo seems to lack clarity on how the resultant loss translates to an increased focus on harder examples, compared to Categorical Crossentropy Loss.

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 82.47%. Comparing base (6e688ab) to head (fa89ab0).

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #21044   +/-   ##
=======================================
  Coverage   82.47%   82.47%           
=======================================
  Files         563      563           
  Lines       53834    53834           
  Branches     8359     8359           
=======================================
  Hits        44401    44401           
  Misses       7392     7392           
  Partials     2041     2041           

Flag	Coverage Δ
keras	82.29% <ø> (ø)
keras-jax	63.79% <ø> (ø)
keras-numpy	58.75% <ø> (ø)
keras-openvino	32.71% <ø> (ø)
keras-tensorflow	64.11% <ø> (ø)
keras-torch	63.83% <ø> (ø)

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