Fix dependencies between rust-mode implementations

"rust-prog-mode.el" and "rust-mode-treesitter.el" provide competing
implementations of `rust-mode'.  Both implementations depend on code
in "rust-mode.el", and thus must require that.

Doing that is complicated by the fact that "rust-mode.el" loads one
of these libraries, depending on `rust-mode-treesitter-derive's value.

Address this conflict by:

1. Requiring feature `rust-mode' in the two libraries that implement the
   `rust-mode' major-mode and that use things defined in "rust-mode.el".

2. Moving the require forms for these two libraries in "rust-mode.el",
   below the `provide' form for `rust-mode'.

0 files changed, 0 insertions, 0 deletions