Added new documentation for code in symfunc module #3413

Job	Run time
conda / conda (ubuntu-20.04)	11m 42s
docker / docker (fedora39)	20m 0s
conda / conda (macos-13)	24m 46s
codecheck / codecheck	43m 47s
docker / docker (rocky8)	24m 33s
conda / conda (macos-14)	7m 18s
linux / linux (-doc-mpi-)	33m 21s
linux / linux (-mpi-)	52m 26s
linux / linux (-coverage-mpi-)	1h 2m 56s
mac / macsimple (macos-13)	13m 41s
linux / linux (-debug-)	46s
mac / macports (macos-13)	23m 19s
mac / macsimple (macos-14)	4m 46s
linux / linux (-debug-mpi-)	44s
mac / macports (+allmodules, macos-13)	34m 11s
linux / linux (-intel-)	47m 13s
linux / linux (-pycv-mpi-)	18m 59s
linux / linux (-nvhpc-mpi-)	57m 59s
	8h 2m 27s

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