Ensure that dev-env is in PATH for other dev-env tools (#2127)

This is relevant for users of the IntelliJ bazel plugin. It is common to
start IntelliJ via the GUI such that the dev-env is not loaded for
IntelliJ. The bazel plugin is then configured to execute the dev-env
bazel by entering the path into the corresponding configuration option.
However, this bazel is then executed without the dev-env tools in PATH.
Some of the repository rules expect certain dev-env tools in PATH, e.g.
python3. Those will then fail.

This patch ensures that the dev-env is loaded when executing dev-env
tools from outside the dev-env.

dev-env/lib/dade-common

@@ -127,6 +127,8 @@ execTool() {
   local outputName=$2
   local binary=$3
   shift 3
+  [[ $PATH =~ (^|.*:)$DADE_DEVENV_DIR/bin($|:.*) ]] || \
+    eval "$(${DADE_DEVENV_DIR}/bin/dade assist)"
   buildTool $attr $outputName 0
   exec "$(readlink "$DADE_BUILD_RESULT")/bin/$binary" "$@"
 }