…clauses-on-ty-aliases, r=compiler-errors

Detect empty leading where clauses on type aliases

1. commit: refactor the AST of type alias where clauses
   * I could no longer bear the look of `.0.1` and `.1.0`
   * Arguably moving `split` out of `TyAlias` into a substruct might not make that much sense from a semantic standpoint since it reprs an index into `TyAlias.predicates` but it's alright and it cleans up the usage sites of `TyAlias`
2. commit: fix an oversight: An empty leading where clause is still a leading where clause
   * semantically reject empty leading where clauses on lazy type aliases
     * e.g., on `#![feature(lazy_type_alias)] type X where = ();`
   * make empty leading where clauses on assoc types trigger lint `deprecated_where_clause_location`
     * e.g., `impl Trait for () { type X where = (); }`

…iaskrgr

Rollup of 5 pull requests

Successful merges:

 - rust-lang#110543 (Make `ReentrantLock` public)
 - rust-lang#121689 ([rustdoc] Prevent inclusion of whitespace character after macro_rules ident)
 - rust-lang#121724 (Use `LitKind::Err` for malformed floats)
 - rust-lang#121735 (pattern analysis: Don't panic when encountering unexpected constructor)
 - rust-lang#121743 (Opportunistically resolve regions when processing region outlives obligations)

Failed merges:

 - rust-lang#121326 (Detect empty leading where clauses on type aliases)
 - rust-lang#121416 (Improve error messages for generics with default parameters)
 - rust-lang#121669 (Count stashed errors again)
 - rust-lang#121723 (Two diagnostic things)

r? `@ghost`
`@rustbot` modify labels: rollup

…iaskrgr

Rollup of 8 pull requests

Successful merges:

 - rust-lang#121326 (Detect empty leading where clauses on type aliases)
 - rust-lang#121464 (rustc: Fix wasm64 metadata object files)
 - rust-lang#121681 (Safe Transmute: Revise safety analysis)
 - rust-lang#121753 (Add proper cfg to keep only one AlignmentEnum definition for different target_pointer_widths)
 - rust-lang#121782 (allow statics pointing to mutable statics)
 - rust-lang#121798 (Fix links in rustc doc)
 - rust-lang#121806 (add const test for ptr::metadata)
 - rust-lang#121809 (Remove doc aliases to PATH)

r? `@ghost`
`@rustbot` modify labels: rollup

Rollup merge of rust-lang#121326 - fmease:detect-empty-leading-where-clauses-on-ty-aliases, r=compiler-errors

Detect empty leading where clauses on type aliases

1. commit: refactor the AST of type alias where clauses
   * I could no longer bear the look of `.0.1` and `.1.0`
   * Arguably moving `split` out of `TyAlias` into a substruct might not make that much sense from a semantic standpoint since it reprs an index into `TyAlias.predicates` but it's alright and it cleans up the usage sites of `TyAlias`
2. commit: fix an oversight: An empty leading where clause is still a leading where clause
   * semantically reject empty leading where clauses on lazy type aliases
     * e.g., on `#![feature(lazy_type_alias)] type X where = ();`
   * make empty leading where clauses on assoc types trigger lint `deprecated_where_clause_location`
     * e.g., `impl Trait for () { type X where = (); }`

…clauses-on-ty-aliases, r=compiler-errors

Detect empty leading where clauses on type aliases

1. commit: refactor the AST of type alias where clauses
   * I could no longer bear the look of `.0.1` and `.1.0`
   * Arguably moving `split` out of `TyAlias` into a substruct might not make that much sense from a semantic standpoint since it reprs an index into `TyAlias.predicates` but it's alright and it cleans up the usage sites of `TyAlias`
2. commit: fix an oversight: An empty leading where clause is still a leading where clause
   * semantically reject empty leading where clauses on lazy type aliases
     * e.g., on `#![feature(lazy_type_alias)] type X where = ();`
   * make empty leading where clauses on assoc types trigger lint `deprecated_where_clause_location`
     * e.g., `impl Trait for () { type X where = (); }`