Update documentation for legacyconversions.
Update documentation for legacyconversions.

This new documentation reflects the ongoing refactorings which pull legacyconversions from libraries to callers.

RELNOTES:Documentation for goog.html.legacyconversions is updated to reflect the new contract for these functions. Previously they were meant just for libraries, now they are also meant for application code. There are however no API changes.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=114526253

federkasten/closure-library,google/closure-library,codyebberson/closure-library,teppeis/closure-library,redforks/closure-library,joeltine/closure-library,ChadKillingsworth/closure-library,lucidsoftware/closure-library,ralic/closure-library,lucidsoftware/closure-library,ikabirov/closure-library,joeltine/closure-library,Dominator008/closure-library,google/closure-library,teppeis/closure-library,ralic/closure-library,joeltine/closure-library,teppeis/closure-library,lucidsoftware/closure-library,Medium/closure-library,redforks/closure-library,federkasten/closure-library,google/closure-library,codyebberson/closure-library,federkasten/closure-library,Medium/closure-library,codyebberson/closure-library,ChadKillingsworth/closure-library,platinumpixs/google-closure-library,lucidsoftware/closure-library,ikabirov/closure-library,google/closure-library,Dominator008/closure-library,Dominator008/closure-library,redforks/closure-library,ChadKillingsworth/closure-library,Medium/closure-library,ralic/closure-library,Dominator008/closure-library,federkasten/closure-library,platinumpixs/google-closure-library,codyebberson/closure-library,ChadKillingsworth/closure-library,joeltine/closure-library,ralic/closure-library,platinumpixs/google-closure-library,teppeis/closure-library,platinumpixs/google-closure-library,ikabirov/closure-library,google/closure-library,Medium/closure-library,redforks/closure-library,ikabirov/closure-library