feat: Add missing SyntaxFactory constructors to unblock assist migrations

[akashchakrabortymsc-cmd]

While working on the assist migration tracking issue #18285, I attempted
to migrate move_bounds.rs and remove_unused_imports.rs to use the
SyntaxEditor API. Both migrations are currently blocked because
SyntaxFactory is missing several constructors and methods that are
still only available in the old edit_in_place / make API.

Missing Methods

move_bounds.rs blocker

• where_pred() — constructs a WherePred node from a target
  (Either<Lifetime, Type>) and an iterator of TypeBound
• get_or_create_where_clause() — finds or inserts a WhereClause
  on AST nodes like Fn, Trait, Impl, Enum, Struct, TypeAlias

remove_unused_imports.rs blocker

• UseTree::remove_recursive() — removes a UseTree node and cleans
  up parent braces, trailing commas, and empty use statements

split_import.rs blocker

• UseTree::split_prefix() — splits a use path at a given prefix
  into a braced subtree

Proposed Fix

Implement these in:

crates/syntax/src/ast/syntax_factory/constructors.rs

and the relevant SyntaxEditor extension traits.

Before proceeding — is this the right approach, or are these
intentionally deferred? Happy to take this on if it looks good.

References

• Migrate assists to SyntaxEditor #18285

[A4-Tacks]

move_bound has been migrated in the #21734

Migrated edit method add to crates/syntax/src/syntax_editor/edits.rs

[A4-Tacks]

Usually, these methods are written by yourself when you need to use them

[akashchakrabortymsc-cmd]

@A4-Tacks THANKS for the clarification ..

can i work on remove_unused_imports

[A4-Tacks]

You can, but it may be a bit challenging

[akashchakrabortymsc-cmd]

i can understand.. yet help me to learn a lot so i think its worth giving a try .. should i open a new issue or started doing here ??

[A4-Tacks]

started doing here