lib/common: add character width lookup tables for more fonts and variants

lib/common: add character width lookup tables for more fonts and variants

This allows Graphviz to estimate the widths of text spans more accurately when built without a textlayout plugin. The textlayout plugins are platform-specific and can be difficult to build for obscure platforms (e.g. Graphviz Online), resulting in node labels not fitting within their nodes nicely.

lib/common: add new source file and header

lib/common: don't install new header

lib/common: redesign hard-coded font metrics

lib/common: remove unused variables

lib/common: format new source file with clang-format

lib/common: add more fonts

lib/common: add warning spam guards

lib/common: improve code style and comments

lib/common: improve code style and comments

lib/common: fix const compiler error

lib/common: reuse existing isalpha_no_locale function

lib/common: fix another const compilation error

lib/common: fix yet another const compilation error

update changelog

update changelog