CompileScript parseOnly mode

Editor assessment

feat(compiler-sfc) introduces a compileScript parseOnly mode, which is a clear statement of the new capability. The short body notes it is an internal feature meant for IDE support, supplying the reason the mode exists and who benefits, which is useful context rather than a restatement. Type and scope are accurate. No footers are needed for an additive, non-breaking change. The message is imperative, unterminated, and free of clutter. Slightly terse, but it explains the purpose and is readily publishable.