Fix whitespace after fragment specifiers in macro pretty printing

When a macro-generating-macro captures fragment specifier tokens (like
`$x:ident`) as `tt` metavariables and replays them before a keyword
(like `where`), the pretty printer concatenates them into an invalid
fragment specifier (e.g. `$x:identwhere` instead of `$x:ident where`).

This happens because `tt` captures preserve the original token spacing.
When the fragment specifier name (e.g. `ident`) was originally the last
token before a closing delimiter, it retains `JointHidden` spacing. The
`print_tts` function only checks `space_between` for `Spacing::Alone`
tokens, so `JointHidden` tokens skip the space check entirely, causing
adjacent identifier-like tokens to merge.

The fix adds a check in `print_tts` to insert a space between adjacent
identifier-like tokens (identifiers and keywords) regardless of the
original spacing, preventing them from being concatenated into invalid
tokens.

This is similar to the existing `space_between` mechanism that prevents
token merging for `Spacing::Alone` tokens, extended to also handle
`Joint`/`JointHidden` cases where two identifier-like tokens would merge.

Signed-off-by: Andrew V. Teylu <andrew.teylu@vector.com>