Do not drop empty arguments in Bun.spawn

[pjeweb]

What does this PR do?

This will not drop empty string arguments passed to Bun.spawn().

• Documentation or TypeScript types (it's okay to leave the rest blank in this case)
• Code changes

How did you verify your code works?

• I checked the lifetime of memory allocated to verify it's (1) freed and (2) only freed when it should be
• I included a test for the new code, or an existing test covers it
• JSValue used outside outside of the stack is either wrapped in a JSC.Strong or is JSValueProtect'ed
• I wrote TypeScript/JavaScript tests and they pass locally (bun-debug test test-file-name.test)

Resolves #13197