Rather than update library symbols one at a time, queue them up by
schematic symbol to prevent multiple updates to the same symbol in
complex hierarchies. This also removes all of the library symbols
first which will clear out all of the library symbol variants that
were created by modifying library symbols in place and/or changes to
the symbol in the library.
Don't add new variant library symbol if an equivalent variant already
exists in the schematic local cache. This prevents duplicate library
symbols from being added to the local cache when the first variant in
the cache does not match that of the symbol being added.
ADDED Update Symbol from Library and Change Symbol can now specify
whether or not to update attributes (include in BOM and include on
board).
Fixes https://gitlab.com/kicad/code/kicad/issues/7123
Also makes sure that the instance fields get set for reference, value
and footprint, and not just the base SCH_FIELD.
Also makes the translations easier.
Fixes https://gitlab.com/kicad/code/kicad/issues/6459
Jeff Young
Wayne Stambaugh