Prefer explicit construction to coercion in record initialization

While we support initializing records via coercion from an expression
list, e.g.,

    local x: X = [$x1=1, $x2=2];

this can sometimes obscure the code to readers, e.g., when assigning to
value declared and typed elsewhere. The language runtime has a similar
overhead since instead of just constructing a known type it needs to
check at runtime that the coercion from the expression list is valid;
this can be slower than just writing the readible code in the first
place, see #4559.

With this patch we use explicit construction, e.g.,

    local x = X($x1=1, $x2=2);

scripts/base/utils/patterns.zeek

@@ -61,7 +61,7 @@ function match_pattern(s: string, p: pattern): PatternMatchResult
 
 	if ( |a| == 1 )
 		# no match
-		return [$matched = F, $str = "", $off = 0];
+		return PatternMatchResult($matched = F, $str = "", $off = 0);
 	else
-		return [$matched = T, $str = a[1], $off = |a[0]| + 1];
+		return PatternMatchResult($matched = T, $str = a[1], $off = |a[0]| + 1);
 	}