lib/kargs: Make API public and upstream new rpm-ostree APIs

This change makes public the current kargs API in src/libostree/ostree-kernel-args.c
and adds documentations.

Upstreams the new kargs API from rpm-ostree/src/libpriv/rpmostree-kargs-process.c

Merges libostree_kernel_args_la_SOURCES to libostree_1_la_SOURCES in Makefile-libostree.am

Upstreams tests/check/test-kargs.c from rpm-ostree.

Closes: #1833

Closes: #1869
Approved by: jlebon

apidoc/Makefile.am

@@ -78,7 +78,6 @@ IGNORE_HFILES= \
 	ostree-fetcher.h \
 	ostree-gpg-verifier.h \
 	ostree-gpg-verify-result-private.h \
-	ostree-kernel-args.h \
 	ostree-libarchive-input-stream.h \
 	ostree-lzma-compressor.h \
 	ostree-lzma-decompressor.h \

apidoc/ostree-sections.txt

@@ -669,3 +669,25 @@ ostree_repo_set_collection_ref_immediate
 ostree_repo_transaction_set_collection_ref
 ostree_repo_resolve_collection_ref
 </SECTION>
+
+<SECTION>
+<FILE>ostree-kernel-args</FILE>
+OstreeKernelArgs
+ostree_kernel_args_free
+ostree_kernel_args_new
+ostree_kernel_args_cleanup
+ostree_kernel_args_replace_take
+ostree_kernel_args_replace
+ostree_kernel_args_replace_argv
+ostree_kernel_args_append
+ostree_kernel_args_append_argv
+ostree_kernel_args_append_argv_filtered
+ostree_kernel_args_new_replace
+ostree_kernel_args_delete
+ostree_kernel_args_delete_key_entry
+ostree_kernel_args_append_proc_cmdline
+ostree_kernel_args_parse_append
+ostree_kernel_args_from_string
+ostree_kernel_args_to_strv
+ostree_kernel_args_to_string
+</SECTION>