compiler: minor inference adjustments (#54420)
This PR consists of a collection of minor adjustments to inference. I've
tried to ensure that the purpose of each change is communicated by each
commit message.
- tfuncs: cosmetic changes (63bdfe0addf71eee8250ea3e5aa87251ad28b305)
* rm no longer necessary type assertions
* rm extra newlines
* mk some indents more consistent with the others
- tfuncs: refactor common `varargtype` check into `hasvarargtype`
(b92adff1ecfcb7d561f67f8d63d028212375f0bf)
- tfuncs: improve nothrow modeling of `tuple` and `svec`
(9689fc00d3fb70f84df3812d810356b65ad14739)
- inlining: replace `[builtin|intrinsic]_nothrow` checks with flag-base
ones (ee736aecbdc76e57f1ae9c0ea53abe642c7925d7)
- tfuncs: rm the weird `UnionAll` special case
(f2f6256770865136cc17f97a393fb4cc92dacc31)
