intellij: add localconfig helper

Adds a little helper tool which merges a watcherTasks template with the local
project config. This restores the functionality lost in D658.

Also cured me of any remaining nostalgic feelings towards XML.

Test Plan:
Deleted all watchers, ran the script, re-opened project,
watchers are back and functional. Local watchers with the same name got
overwritten. Additional watchers were untouched.

X-Origin-Diff: phab/D661
GitOrigin-RevId: 83f7c1506476378145781c816d776fd451aed40c
diff --git a/intellij/localconfig/watchers/BUILD.bazel b/intellij/localconfig/watchers/BUILD.bazel
new file mode 100644
index 0000000..bae47c7
--- /dev/null
+++ b/intellij/localconfig/watchers/BUILD.bazel
@@ -0,0 +1,8 @@
+load("@io_bazel_rules_go//go:def.bzl", "go_library")
+
+go_library(
+    name = "go_default_library",
+    srcs = ["filewatchers.go"],
+    importpath = "git.monogon.dev/source/nexantic.git/intellij/localconfig/watchers",
+    visibility = ["//visibility:public"],
+)