Fix various occurrence var names and references

[ryanrussell]

Signed-off-by: Ryan Russell git@ryanrussell.org

Vars re-mapped:

• expected_ids_and_num_occurrences
• id_occurrences

Also a few loose doc references were fixed.

[codecov-commenter]

Codecov Report

Merging #1385 (9c82659) into main (5e599d9) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main    #1385   +/-   ##
=======================================
  Coverage   94.26%   94.27%           
=======================================
  Files         235      235           
  Lines       42896    42896           
=======================================
+ Hits        40437    40439    +2     
+ Misses       2459     2457    -2     

Impacted Files	Coverage Δ
src/query/boolean_query/boolean_query.rs	92.56% <ø> (ø)
src/schema/index_record_option.rs	100.00% <ø> (ø)
src/indexer/index_writer.rs	96.74% <100.00%> (ø)
src/fastfield/reader.rs	89.91% <0.00%> (+0.84%)	⬆️
src/directory/watch_event_router.rs	96.63% <0.00%> (+0.84%)	⬆️

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