Add optional ICU support for user search (#14464)

Fixes #13655

This change uses ICU (International Components for Unicode) to improve boundary detection in user search.

This change also adds a new dependency on libicu-dev and pkg-config for the Debian packages, which are available in all supported distros.

docker/Dockerfile

@@ -97,6 +97,8 @@ RUN \
     zlib1g-dev \
     git \
     curl \
+    libicu-dev \
+    pkg-config \
     && rm -rf /var/lib/apt/lists/*
 
 

docker/Dockerfile-dhvirtualenv

@@ -84,6 +84,8 @@ RUN apt-get update -qq -o Acquire::Languages=none \
         python3-venv \
         sqlite3 \
         libpq-dev \
+        libicu-dev \
+        pkg-config \
         xmlsec1
 
 # Install rust and ensure it's in the PATH