Repurposed FDMap as Remap then subclassed for remapping SIDs
misc code cleanup

Added hb-ot-cff1-table.cc to hb-subset sources
Deleted unused variable (charset)

Added HB_INTERNAL to static funtion declarations

fixed misc Charset bugs
added source file hb-ot-cff1.table.cc
renamed things for clarity & consistency

They are still in the drop list.

as they aren't instantiated with BlendArg (yet)

Templatized ArgStack so it may store the default value along with blend deltas as BlendArg while parsing blend operator arguments in CFF2 charstring
Added get_region_count() method to VarRegionList & VariationStore

Should remove the vector version at some point...

Why does subset plan not have a hb_set_t of glyphs?

Ouch.

Remove Lookup::subset().

Add subset() call for GSUBGPOS struct and its dependencies.
Not hooked up anywhere.

We're going to (finally) use virtual methods for hb_serialize_context_t
customization, so don't need to carry a Serializer template variable
around...  Simplifies code.

renamed confusing Stack.size to Stack.count

Factored out CFF1 & CFF2 common subsetting code in hb-subset-cff-common.hh

We might reintroduce it later, but for now remove, as it was unused.
Some things that should have been in this object (drop_hints, etc)
are already in hb_subset_input_t.  So, for now, keep everything there.

Fixes https://github.com/harfbuzz/harfbuzz/issues/1145

pkg.m4 is provided by pkg-config, which is a requirement to build, and this copy is ancient.  Delete it to avoid it being used instead of the host copy.