Move RcuVector and relevant support classes to vespalib

Having RCU support available across all our C++ modules open up
new opportunities for optimizations.

This changes the following:
- `RcuVector` moved from `searchlib` to `vespalib`
- `MemoryUsage` moved from `searchlib` to `vespalib`
- Introduce a simplified, more generic `GrowStrategy` in `vespalib`
  used by the moved `RcuVector` which does not have any notion of
  documents. Existing searchlib `GrowStrategy` gets a simple function
  to convert to this generic strategy.

1 files changed, 1 insertions, 0 deletions

diff --git a/searchlib/src/tests/memoryindex/compact_words_store/compact_words_store_test.cpp b/searchlib/src/tests/memoryindex/compact_words_store/compact_words_store_test.cpp
index 04d66396f90..a78e4dead86 100644
--- a/searchlib/src/tests/memoryindex/compact_words_store/compact_words_store_test.cpp
+++ b/searchlib/src/tests/memoryindex/compact_words_store/compact_words_store_test.cpp
@@ -11,6 +11,7 @@
 using namespace search;
 using namespace search::datastore;
 using namespace search::memoryindex;
+using vespalib::MemoryUsage;
 
 typedef CompactWordsStore::Builder Builder;
 typedef CompactWordsStore::Iterator Iterator;