treewide: revise library packaging

- Annotate versionless libraries (such as libubox, libuci etc.) with a fixed
  ABI_VERSION resembling the source date of the last incompatible change
- Annotate packages shipping versioned library objects with ABI_VERSION
- Stop shipping unversioned library symlinks for packages with ABI_VERSION

Ref: https://openwrt.org/docs/guide-developer/package-policies#shared_libraries
Ref: https://github.com/KanjiMonster/maintainer-tools/blob/master/check-abi-versions.pl
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

package/libs/libjson-c/Makefile

@@ -9,7 +9,7 @@ include $(TOPDIR)/rules.mk
 
 PKG_NAME:=json-c
 PKG_VERSION:=0.12.1
-PKG_RELEASE:=2
+PKG_RELEASE:=3
 
 PKG_SOURCE:=$(PKG_NAME)-$(PKG_VERSION)-nodoc.tar.gz
 PKG_SOURCE_URL:=https://s3.amazonaws.com/json-c_releases/releases/
@@ -38,6 +38,7 @@ define Package/libjson-c
   CATEGORY:=Libraries
   TITLE:=javascript object notation
   URL:=https://json-c.github.io/json-c/
+  ABI_VERSION:=2
 endef
 
 define Package/libjson-c/description