Use cached StringBuilder in CreateManifestResourceName

[ladipro]

Fixes #5551

Context

Addressing a small inefficiency pointed out in #5551. If the task is given multiple resource files it wastefully creates a new StringBuilder for each.

Changes Made

Reuse a cached StringBuilder when creating resource names.

Testing

Existing unit tests.

Notes

• The StringBuilder is not used "append-only" so this is not a good fit for SpanBasedStringBuilder.
• I did not put the release call inside a finally block because if the code throws an exception "leaking" a StringBuilder is not a big deal with very minor perf impact compared to the exception handling machinery.