Latvian: finally handles PassV2 clauses in a more or less adequate way

Extends the previously introduced support for specifying the verb valence (verb-dependent subject and object cases), involving functions up to PredVP and RelVP.

In Latvian, the passive voice is not used if the agent (subject) is known; to preserve the information structure (i.e. the word order), a clause like 'A is <done> by B' is linearized in the active voice ('A <does> B') where A has the object case (e.g. Acc), and B - the subject case (e.g. Nom). Thus, the verb valence patterns are swapped on-the-fly.

This is still a rather quick & dirty implementation: parameters and linearization types have to be optimized (VerbLav), the use of PassV2 in AdvVP is problematic as it doesn't apply VPSlashPrep / ComplSlash, etc.

lib/src/latvian/AdjectiveLav.gf

@@ -18,7 +18,7 @@ lin
   UseComparA a = { s = \\d,g,n,c => a.s ! (AAdj Compar d g n c) } ;
 
   ComplA2 a np = {
-    s = \\d,g,n,c => a.s ! (AAdj Posit d g n c) ++ a.p.s ++ np.s ! (a.p.c ! (fromAgr np.a).n)
+    s = \\d,g,n,c => a.s ! (AAdj Posit d g n c) ++ a.p.s ++ np.s ! (a.p.c ! (fromAgr np.a).num)
   } ;
 
   ReflA2 a = { s = \\d,g,n,c => a.s ! (AAdj Posit d g n c) ++ a.p.s ++ reflPron ! (a.p.c ! n) } ;