'Convert to manual ...' code action doesn't send the missing members code when snippetTextEdits are disabled

[simrat39]

Pretty much the title.

Without snippet text edits enabled:

With:

References: https://github.com/simrat39/rust-tools.nvim/issues/53 https://github.com/simrat39/rust-tools.nvim/issues/60

[DropDemBits]

On the match arm that handles when snippetTextEdits is unavailable, it ignores whether impl_def_with_items is Some, which is important since impl_def_with_items contains the impl with the correct missing members. https://github.com/rust-lang/rust-analyzer/blob/ea7fdada6a0940b239ddbde2048a4d7dac1efe1e/crates/ide-assists/src/handlers/replace_derive_with_manual_impl.rs#L147-L155

The other match arms correctly deal with impl_def_with_items but only differ in that they add snippets. Ideally this match arm should be removed and the snippet capability handling moved inside of the other two match arms.

[Samarth1696]

I am ok to take the issue.