Periodic documentation update

The edits in this set include:

Updated the section on inheritance in the Editions Overview topic to use the more-accurate term "lexical scoping."
In the extension declarations topic, added clarification about using the full_name of a reserved field
In the proto3 topic, added information about positive and negative zero in floats and doubles
In the proto3 topic, added information about what files Kotlin generates and what they do
In the proto3 topic, updates content about how unknown fields are handled to match current functionality
Adds information to the Java topic about nested builder functionality that is not available in the Lite version
Adds a section about unknown fields to the textformat spec topic
Adds the proposed way to handle repeated message field assignments (previously only the ways NOT to do it were in the code sample)

PiperOrigin-RevId: 587099048 Change-Id: Id2a3709931ac12726a629f489ceffce27341fc6f

protocolbuffers / protocolbuffers.github.io