Add String Formatting Util

(Merged from http://go/wvgerrit/160042.)

Since we don't have access to std::format yet, this patch adds a
function to wvutil to format text into a std::string.

Bug: 255466913
Test: x86-64
Test: raven
Change-Id: I28043da76af5b4772a29fa7e7241343caf9b54a1

libwvdrmengine/Android.bp

@@ -309,6 +309,7 @@ cdm_util_src_files = [
     "cdm/util/src/platform.cpp",
     "cdm/util/src/rw_lock.cpp",
     "cdm/util/src/string_conversions.cpp",
+    "cdm/util/src/string_format.cpp",
 ]
 
 cc_library_static {