pallet macro: do not generate try-runtime related code when frame-support...

pallet macro: do not generate try-runtime related code when frame-support doesn't have try-runtime. (#5099)

Status: Ready for review

Fix https://github.com/paritytech/polkadot-sdk/issues/5092

Introduce a new macro in frame-support which discard content if
`try-runtime` is not enabled.

Use this macro inside `frame-support-procedural` to generate code only
when `frame-support` is compiled with `try-runtime`.

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Co-authored-by: Bastian Köcher <git@kchr.de>