Emit a single error for contiguous sequences of unknown tokens
Closes#106101
On encountering a sequence of identical source characters which are unknown tokens, note the amount of subsequent characters and advance past them silently. The old behavior was to emit an error and 'help' note for every single one.
`@rustbot` label +A-diagnostics +A-parser
Render missing generics suggestion verbosely
It's a bit easier to read like this, especially ones that are appending new generics onto an existing list, like ": `, T`" which render somewhat poorly inline.
Also don't suggest `dyn` as a type parameter to add, even if technically that's valid in edition 2015.
Recover from where clauses placed before tuple struct bodies
Open to any suggestions regarding the phrasing of the diagnostic.
Fixes#100790.
`@rustbot` label A-diagnostics
r? diagnostics
