Add tools/sync-bazelversion.sh, commit results

Part of bazelbuild#1482.

Ensures Bazelisk uses the same Bazel version in every workspace in the
project.

I discovered that the workspaces under the main workspace were running
the latest mainline Blaze release I had installed. Now all the
workspaces are synchronized on the same Bazel version.

As noted in the `tools/sync-bazelversion.sh` comments, symlinks or an
`import ../.bazelversion` mechanism would be preferable. However, the
former can surprise Windows users, and Bazelisk doesn't support the
latter.

dt_patches/test_dt_patches/.bazelversion

@@ -1 +1 @@
-5.3.1
+6.5.0

dt_patches/test_dt_patches_user_srcjar/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/crossbuild/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/scala3/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/semanticdb/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/testing/multi_frameworks_toolchain/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/testing/scalatest_repositories/.bazelversion

@@ -0,0 +1 @@
+6.5.0

examples/testing/specs2_junit_repositories/.bazelversion

@@ -0,0 +1 @@
+6.5.0

test_cross_build/.bazelversion

@@ -0,0 +1 @@
+6.5.0

test_version/.bazelversion

@@ -0,0 +1 @@
+6.5.0

third_party/test/example_external_workspace/.bazelversion

@@ -0,0 +1 @@
+6.5.0

third_party/test/proto/.bazelversion

@@ -0,0 +1 @@
+6.5.0

tools/sync-bazelversion.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+#
+# Synchronizes .bazelversion in nested workspaces with the top level workspace.
+#
+# These could be symlinks, but that might break Windows users who don't know how
+# to enable symlinks. Of course, they're programmers, they should learn, but
+# avoiding surprises as a general principle is best.
+#
+# What would be ideal is the `import ../.bazelrc` syntax supported by Bazel, but
+# Bazelisk doesn't currently support that.
+
+ROOTDIR="${BASH_SOURCE[0]%/*}/.."
+cd "$ROOTDIR"
+
+if [[ "$?" -ne 0 ]]; then
+ echo "Could not change to $ROOTDIR." >&2
+ exit 1
+elif [[ ! -r .bazelversion ]]; then
+ echo ".bazelversion doesn't exist or isn't readable in $PWD." >&2
+ exit 1
+fi
+
+while IFS="" read rcpath; do
+ cp .bazelversion "${rcpath%/*}"
+done < <(find [a-z]* -name '.bazelrc')