add thread-unsafe warnings to data docs

closes PR 13367, closes PR 13369

collects/data/scribblings/gvector.scrbl

@@ -26,6 +26,8 @@ number of elements in the gvector.
 Two gvectors are @racket[equal?] if they contain the same number of
 elements and if the contain equal elements at each index.
 
+Operations on gvectors are not thread-safe.
+
 @defproc[(make-gvector [#:capacity capacity exact-positive-integer? 10])
          gvector?]{
 

collects/data/scribblings/heap.scrbl

@@ -15,6 +15,8 @@
 
 Binary heaps are a simple implementation of priority queues.
 
+Operations on binary heaps are not thread-safe.
+
 @defproc[(make-heap [<=? (-> any/c any/c any/c)])
          heap?]{
 

collects/data/scribblings/interval-map.scrbl

@@ -39,6 +39,8 @@ end positions of the mapping's intervals.
 (dict-map r list)
 ]
 
+Operations on interval-maps are not thread-safe.
+
 @defproc[(make-interval-map [#:key-contract key-contract contract? any/c]
                             [#:value-contract value-contract contract? any/c])
          interval-map?]{

collects/data/scribblings/skip-list.scrbl

@@ -24,6 +24,11 @@ A skip-list is an ordered dictionary (@racket[dict?] and
 @racket[ordered-dict?]). It also supports extensions of the dictionary
 interface for iterator-based search and mutation.
 
+Operations on skip-lists are not thread-safe. If a key in a skip-list
+is mutated, the skip-list's internal invariants may be violated,
+causings its behavior to become unpredictable.
+
+
 @defproc[(make-skip-list [ord order? datum-order]
                          [#:key-contract key-contract contract? any/c]
                          [#:value-contract value-contract contract? any/c])

collects/data/scribblings/splay-tree.scrbl

@@ -23,6 +23,11 @@ Tarjan in Journal of the ACM 32(3) pp652-686.
 A splay-tree is a ordered dictionary (@racket[dict?] and
 @racket[ordered-dict?]).
 
+Operations on splay-trees are not thread-safe. If a key in a
+splay-tree is mutated, the splay-tree's internal invariants may be
+violated, causing its behavior to become unpredictable.
+
+
 @defproc[(make-splay-tree [ord order? datum-order]
                           [#:key-contract key-contract contract? any/c]
                           [#:value-contract value-contract contract? any/c])