frontend: make fn calls byval; fix false positive isNonErr

[andrewrk]

This commit does two things which seem unrelated at first, but, together, solve a miscompilation, and potentially slightly speed up compiler perf, at the expense of making #2765 trickier to implement in the future.

Sema: avoid returning a false positive for whether an inferred error set is comptime-known to be empty.

AstGen: mark function calls as not being interested in a result location. This prevents the test case "ret_ptr doesn't cause own inferred error set to be resolved" from being regressed. If we want to accept and implement #2765 in the future, it will require solving this problem a different way, but the principle of YAGNI tells us to go ahead with this change.

Old ZIR looks like this:

%97 = ret_ptr()
%101 = store_node(%97, %100)
%102 = load(%97)
%103 = ret_is_non_err(%102)

New ZIR looks like this:

%97 = ret_type()
%101 = as_node(%97, %100)
%102 = ret_is_non_err(%101)

closes #15669

[andrewrk]

potentially slightly speed up compiler perf

Data point for building the compiler itself:

Benchmark 1 (3 runs): before/zig build-exe ...
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          60.5s  ±  223ms    60.3s  … 60.7s           0 ( 0%)        0%
  peak_rss           3.87GB ± 31.5MB    3.85GB … 3.91GB          0 ( 0%)        0%
  cpu_cycles          248G  ± 1.60G      246G  …  250G           0 ( 0%)        0%
  instructions        357G  ± 1.73G      356G  …  359G           0 ( 0%)        0%
  cache_references   14.4G  ± 15.8M     14.3G  … 14.4G           0 ( 0%)        0%
  cache_misses       1.15G  ± 45.6M     1.12G  … 1.20G           0 ( 0%)        0%
  branch_misses      1.67G  ± 12.2M     1.66G  … 1.68G           0 ( 0%)        0%
Benchmark 2 (3 runs): after/zig build-exe ...
  measurement          mean ± σ            min … max           outliers         delta
  wall_time          61.9s  ± 1.83s     60.3s  … 63.9s           0 ( 0%)          +  2.4% ±  4.9%
  peak_rss           3.84GB ± 28.1MB    3.82GB … 3.87GB          0 ( 0%)          -  0.9% ±  1.7%
  cpu_cycles          248G  ±  818M      247G  …  249G           0 ( 0%)          +  0.0% ±  1.2%
  instructions        357G  ± 1.49G      356G  …  358G           0 ( 0%)          -  0.2% ±  1.0%
  cache_references   14.2G  ± 75.0M     14.1G  … 14.3G           0 ( 0%)          -  0.9% ±  0.9%
  cache_misses       1.17G  ± 67.1M     1.12G  … 1.25G           0 ( 0%)          +  1.6% ± 11.3%
  branch_misses      1.68G  ± 6.62M     1.68G  … 1.69G           0 ( 0%)          +  0.8% ±  1.3%

(insignificant)