Adds a mechanism where when an autoparam tactic fails to synthesize a
parameter, the associated parameter name or field name for the autoparam
is reported in an error.
Examples:
```text
could not synthesize default value for parameter 'h' using tactics
could not synthesize default value for field 'inv' of 'S' using tactics
```
Notes:
* Autoparams now run their tactics without any error recovery or
error-to-sorry enabled. This enables catching the error and reporting
the contextual information. This is justified on the grounds that
autoparams are not interactive.
* Autoparams for applications now cleanup the autoParam annotation,
bringing it in line with autoparams for structure fields.
* This preserves the old behavior that autoparams leave terminfo, but we
will revisit this after some imminent improvements to the unused
variable linter.
Closes#2950
Defines `mergeSort`, a naive stable merge sort algorithm, replaces it
via a `@[csimp]` lemma with something faster at runtime, and proves the
following results:
* `mergeSort_sorted`: `mergeSort` produces a sorted list.
* `mergeSort_perm`: `mergeSort` is a permutation of the input list.
* `mergeSort_of_sorted`: `mergeSort` does not change a sorted list.
* `mergeSort_cons`: proves `mergeSort le (x :: xs) = l₁ ++ x :: l₂` for
some `l₁, l₂`
so that `mergeSort le xs = l₁ ++ l₂`, and no `a ∈ l₁` satisfies `le a
x`.
* `mergeSort_stable`: if `c` is a sorted sublist of `l`, then `c` is
still a sublist of `mergeSort le l`.
