Deprecate Plugin::HookCallFunction(), replace with HookFunctionCall()

This also changes the argument type of Func::operator() to zeek::Args*
to allow plugins to be able to alter function arguments in place as
was previously documented.

testing/btest/plugins/legacy-func-hook.zeek

@@ -0,0 +1,17 @@
+# @TEST-EXEC: ${DIST}/aux/zeek-aux/plugin-support/init-plugin -u . Demo Hooks
+# @TEST-EXEC: cp -r %DIR/legacy-func-hook-plugin/* .
+# @TEST-EXEC: ./configure --zeek-dist=${DIST} && make
+# @TEST-EXEC: ZEEK_PLUGIN_ACTIVATE="Demo::Hooks" ZEEK_PLUGIN_PATH=`pwd` zeek -b %INPUT 2>&1 | grep foo >output
+# @TEST-EXEC: btest-diff output
+
+@unload base/misc/version
+
+function foo(a: count, b: count, c: count, s: string)
+	{
+	print "foo", a, b, c, s;
+	}
+
+event zeek_init()
+	{
+	foo(1, 2, 3, "yo");
+	}