Fix storage expansion in pallet section

[eagr]

fixes #5320 @sam0x17 @gupnik

Description

The issue could be confirmed with the added example. The cause is for macro hygiene, entries in the #( #entries_builder )* expansion won't be able to reference the entries defined outside. The solution here is to allow the reference to be passed into the expansion with closure.

Or we could just switch to the unhygienic span with quote::quote! instead such that entries will resolve to the "outer" definition.

[eagr]

For the added test, without the fix:

test tests/split_ui/pass/split_storage.rs [should pass] ... error
┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈┈
error[E0425]: cannot find value `entries` in this scope
 --> tests/split_ui/pass/storage.rs
  |
  |     #[pallet::storage]
  |               ^^^^^^^ not found in this scope
  |
 ::: tests/split_ui/pass/split_storage.rs:5:1
  |
5 | #[import_section(storage::storage)]
  | ----------------------------------- in this macro invocation
  |
  = note: this error originates in the macro `storage::__export_tokens_tt_storage` which comes from the expansion of the macro `frame_support::macro_magic::forward_tokens` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0425]: cannot find value `entries` in this scope
 --> tests/split_ui/pass/storage.rs
  |
  |     #[pallet::storage]
  |               ^^^^^^^ not found in this scope
  |
 ::: tests/split_ui/pass/split_storage.rs:5:1
  |
5 | #[import_section(storage::storage)]
  | ----------------------------------- in this macro invocation
  |
  = note: this error originates in the macro `storage::__export_tokens_tt_storage` which comes from the expansion of the macro `frame_support::macro_magic::forward_tokens` (in Nightly builds, run with -Z macro-backtrace for more info)

[gui1117]

I'm surprise the code didn't compile.
New code is good, so it is good to me.