tree-wide: add SD_ID128_MAKE_STR, remove LOG_MESSAGE_ID

tree-wide: add SD_ID128_MAKE_STR, remove LOG_MESSAGE_ID

Embedding sd_id128_t's in constant strings was rather cumbersome. We had
SD_ID128_CONST_STR which returned a const char[], but it had two problems:
- it wasn't possible to statically concatanate this array with a normal string
- gcc wasn't really able to optimize this, and generated code to perform the
  "conversion" at runtime.
Because of this, even our own code in coredumpctl wasn't using
SD_ID128_CONST_STR.

Add a new macro to generate a constant string: SD_ID128_MAKE_STR.
It is not as elegant as SD_ID128_CONST_STR, because it requires a repetition
of the numbers, but in practice it is more convenient to use, and allows gcc
to generate smarter code:

$ size .libs/elogind{,-logind,-journald}{.old,}
   text	   data	    bss	    dec	    hex	filename
1265204	 149564	   4808	1419576	 15a938	.libs/elogind.old
1260268	 149564	   4808	1414640	 1595f0	.libs/elogind
 246805	  13852	    209	 260866	  3fb02	.libs/elogind-logind.old
 240973	  13852	    209	 255034	  3e43a	.libs/elogind-logind
 146839	   4984	     34	 151857	  25131	.libs/elogind-journald.old
 146391	   4984	     34	 151409	  24f71	.libs/elogind-journald

It is also much easier to check if a certain binary uses a certain MESSAGE_ID:

$ strings .libs/elogind.old|grep MESSAGE_ID
MESSAGE_ID=%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x
MESSAGE_ID=%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x
MESSAGE_ID=%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x
MESSAGE_ID=%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x%02x

$ strings .libs/elogind|grep MESSAGE_ID
MESSAGE_ID=c7a787079b354eaaa9e77b371893cd27
MESSAGE_ID=b07a249cd024414a82dd00cd181378ff
MESSAGE_ID=641257651c1b4ec9a8624d7a40a9e1e7
MESSAGE_ID=de5b426a63be47a7b6ac3eaac82e2f6f
MESSAGE_ID=d34d037fff1847e6ae669a370e694725
MESSAGE_ID=7d4958e842da4a758f6c1cdc7b36dcc5
MESSAGE_ID=1dee0369c7fc4736b7099b38ecb46ee7
MESSAGE_ID=39f53479d3a045ac8e11786248231fbf
MESSAGE_ID=be02cf6855d2428ba40df7e9d022f03d
MESSAGE_ID=7b05ebc668384222baa8881179cfda54
MESSAGE_ID=9d1aaa27d60140bd96365438aad20286