Share location type strings in memory (#2947)

Memoize location documentation strings to make sure descriptions for
equal types in a single summary are shared in memory.

Motivated by
usethesource/rascal-language-servers#1202,
@DavyLandman and I did an inspection of memory use in Rascal LSP. There
are many duplicate strings in summaries.

Author: toinehartman

src/org/rascalmpl/compiler/lang/rascalcore/check/Summary.rsc

@@ -68,9 +68,13 @@ data ModuleSummary =
                    map[loc def, str synopsis] synopses = (),
                    map[loc def, loc docLoc] docLocs = ());
 
-private map[loc from, str tp] getLocationTypes(TModel tm)
-    = (key : prettyAType(tm.specializedFacts[key] ? tm.facts[key]) | key <- tm.facts);
-    
+private map[loc from, str tp] getLocationTypes(TModel tm) {
+    // Share strings in memory to reduce summary memory pressure
+    @memo str cachedPrettyAType(AType tp) = prettyAType(tp);
+
+    return (key : cachedPrettyAType(tm.specializedFacts[key] ? tm.facts[key]) | key <- tm.facts);
+}
+
 ModuleSummary makeSummary(TModel tm, str qualifiedModuleName) {
     if (!tm.usesPhysicalLocs) {
         tm = convertTModel2PhysicalLocs(tm);