Fix linker error for makeRBSString

The declaration of makeRBSString was added to rbs_common.h (in sorbet#9770)
but the only definition remained inside an anonymous namespace in
SignatureTranslator.cc, making it invisible to other translation units.

Move the definition out of the anonymous namespace and update the
parameter type from `const string &` to `const string_view` to match
the header declaration, so that SignatureTranslatorPrism.cc (and any
future callers) can link against it.

Author: egiurleo

rbs/SignatureTranslator.cc

@@ -9,14 +9,10 @@ using namespace std;
 
 namespace sorbet::rbs {
 
-namespace {
-
-rbs_string_t makeRBSString(const string &str) {
+rbs_string_t makeRBSString(const string_view str) {
     return rbs_string_new(str.data(), str.data() + str.size());
 }
 
-} // namespace
-
 unique_ptr<parser::Node>
 SignatureTranslator::translateAssertionType(vector<pair<core::LocOffsets, core::NameRef>> typeParams,
                                             const rbs::RBSDeclaration &assertion) {