Updates MDCMultilineTextField's bottom textfield constraint to use th…

…e textInsets as the constant.

This brings parallels the calculation done in sizeThatFits and will ensure the set textInsets are always adhered to.

PiperOrigin-RevId: 318268981

components/TextFields/src/MDCMultilineTextField.m

@@ -343,10 +343,11 @@ - (void)updateConstraints {
                                         toItem:self
                                      attribute:NSLayoutAttributeBottom
                                     multiplier:1
-                                      constant:-1 * MDCTextInputHalfPadding];
+                                      constant:-1 * self.textInsets.bottom];
     self.textViewBottomSuperviewBottom.priority = UILayoutPriorityDefaultLow;
     self.textViewBottomSuperviewBottom.active = YES;
   }
+  self.textViewBottomSuperviewBottom.constant = -1 * self.textInsets.bottom;
 
   if (!self.textViewTop) {
     self.textViewTop = [NSLayoutConstraint constraintWithItem:self.textView