kit: implement server components dev server (#14025)

src/string_immutable.zig

@@ -4649,6 +4649,12 @@ pub fn trim(slice: anytype, comptime values_to_strip: []const u8) @TypeOf(slice)
     return slice[begin..end];
 }
 
+pub fn isAllWhitespace(slice: []const u8) bool {
+    var begin: usize = 0;
+    while (begin < slice.len and std.mem.indexOfScalar(u8, &whitespace_chars, slice[begin]) != null) : (begin += 1) {}
+    return begin == slice.len;
+}
+
 pub const whitespace_chars = [_]u8{ ' ', '\t', '\n', '\r', std.ascii.control_code.vt, std.ascii.control_code.ff };
 
 pub fn lengthOfLeadingWhitespaceASCII(slice: string) usize {