Sema: rewrite semantic analysis of function calls

This rewrite improves some error messages, hugely simplifies the logic,
and fixes several bugs. One of these bugs is technically a new rule
which Andrew and I agreed on: if a parameter has a comptime-only type
but is not declared `comptime`, then the corresponding call argument
should not be *evaluated* at comptime; only resolved. Implementing this
required changing how function types work a little, which in turn
required allowing a new kind of function coercion for some generic use
cases: function coercions are now allowed to implicitly *remove*
`comptime` annotations from parameters with comptime-only types. This is
okay because removing the annotation affects only the call site.

Resolves: #22262

lib/std/math/log_int.zig

@@ -61,6 +61,7 @@ pub fn log_int(comptime T: type, base: T, x: T) Log2Int(T) {
 }
 
 test "log_int" {
+    @setEvalBranchQuota(2000);
     // Test all unsigned integers with 2, 3, ..., 64 bits.
     // We cannot test 0 or 1 bits since base must be > 1.
     inline for (2..64 + 1) |bits| {