Split (ninja|soong).mk into config and rule portions

So that an external tool can read the configuration using
dump-many-vars, and write out the soong.variables file while only
loading config.mk.

Also remove dumpvar-% from PARSE_TIME_MAKE_GOALS, since it's only used
with CALLED_FROM_SETUP / config.mk. This provides an easy way to test
this change as well.

Test: get_build_var NINJA
Test: get_build_var ANDROID_GOALS
Test: get_build_var NINJA_GOALS
Test: get_build_var KATI_GOALS
Test: MAKECMDGOALS="droid sdk dumpvar-ANDROID_GOALS" get_build_var ANDROID_GOALS
Test: MAKECMDGOALS="droid sdk dumpvar-NINJA_GOALS" get_build_var NINJA_GOALS
Test: MAKECMDGOALS="droid sdk dumpvar-KATI_GOALS" get_build_var KATI_GOALS
Test: MAKECMDGOALS="out/build-a.ninja dumpvar-ANDROID_GOALS" get_build_var ANDROID_GOALS
Test: get_build_var SOONG_MAKEVARS_MK
Test: get_build_var SOONG_VARIABLES
Test: CALLED_FROM_SETUP=true BUILD_SYSTEM=build/core make -f build/core/config.mk out/soong/soong.variables showcommands
Test: Compare soong.variables from above, and before/after with `m`
Test: Compare out before/after with `m doesnotexist`
Test: `m dist doesnotexist`
Change-Id: I1bc291aa165297c930fe600067edad6ce4979210