fix(site/src/pages/OrganizationSettingsPage): enable sticky positioning for horizontal form sections (#26949)

Followup to #26907, which re-enabled sticky positioning within
`#main-content` throughout the site. From
https://github.com/coder/coder/pull/26907#issuecomment-4860536495:

>Updating [`HorizontalSection` in OrganizationSettingsPageView.tsx]'s
sticky styles will be a little more involved, so I'll save that for a
separate PR.

## before

Note that I inflated this section's height to 1000px in DevTools to be
able to demo sticky positioning not working. This page isn't tall enough
at the moment for the lack of sticky positioning to be much of a
problem. But this will future-proof it (since `FormSection`, whose
sticky styles were fixed in #26907, was built for this purpose) and
allow us to remove some redundant components/files. No other files
imported `HorizontalContainer` or `HorizontalSection`, so
OrganizationSettingsPage/Horizontal.tsx can be safely deleted.

Also note that the **Info** section is sticky as expected, since it was
already using `FormSection`. The **Workspace Sharing** and **Delete
Organization** sections are the ones whose stickiness is fixed by this
PR


https://github.com/user-attachments/assets/9ffed486-87f7-4762-a97a-4268d0328829

## after


https://github.com/user-attachments/assets/581cb33e-50b5-466e-9be9-2518dc22bfa6

site/src/pages/OrganizationSettingsPage/Horizontal.tsx

@@ -1,35 +0,0 @@
-import type { FC, HTMLAttributes, ReactNode } from "react";
-export const HorizontalContainer: FC<HTMLAttributes<HTMLDivElement>> = ({
-	...attrs
-}) => {
-	return <div className="flex flex-col gap-16 md:gap-20" {...attrs} />;
-};
-
-interface HorizontalSectionProps
-	extends Omit<HTMLAttributes<HTMLElement>, "title"> {
-	title: ReactNode;
-	description: ReactNode;
-	children?: ReactNode;
-}
-
-export const HorizontalSection: FC<HorizontalSectionProps> = ({
-	children,
-	title,
-	description,
-	...attrs
-}) => {
-	return (
-		<section className="flex flex-col gap-4 lg:flex-row lg:gap-32" {...attrs}>
-			<div className="w-full shrink-0 lg:sticky lg:top-6 lg:max-w-[312px]">
-				<h2 className="m-0 mb-2 flex flex-row items-center gap-3 text-xl font-normal text-content-primary">
-					{title}
-				</h2>
-				<div className="m-0 text-sm leading-[160%] text-content-secondary">
-					{description}
-				</div>
-			</div>
-
-			{children}
-		</section>
-	);
-};

site/src/pages/OrganizationSettingsPage/OrganizationSettingsPageView.tsx

@@ -33,7 +33,6 @@ import {
 	onChangeTrimmed,
 } from "#/utils/formUtils";
 import { DisableWorkspaceSharingDialog } from "./DisableWorkspaceSharingDialog";
-import { HorizontalContainer, HorizontalSection } from "./Horizontal";
 
 const MAX_DESCRIPTION_CHAR_LIMIT = 128;
 const MAX_DESCRIPTION_MESSAGE = `Please enter a description that is no longer than ${MAX_DESCRIPTION_CHAR_LIMIT} characters.`;
@@ -150,8 +149,8 @@ export const OrganizationSettingsPageView: FC<
 			</HorizontalForm>
 
 			{onChangeShareableOwners && (
-				<HorizontalContainer className="mt-12">
-					<HorizontalSection
+				<HorizontalForm className="mt-12">
+					<FormSection
 						title="Workspace Sharing"
 						description="Control whether workspace owners can share their workspaces."
 					>
@@ -255,13 +254,13 @@ export const OrganizationSettingsPageView: FC<
 								</div>
 							</div>
 						</div>
-					</HorizontalSection>
-				</HorizontalContainer>
+					</FormSection>
+				</HorizontalForm>
 			)}
 
 			{!organization.is_default && (
-				<HorizontalContainer className="mt-12">
-					<HorizontalSection
+				<HorizontalForm className="mt-12">
+					<FormSection
 						title="Delete Organization"
 						description="Delete your organization permanently."
 					>
@@ -277,8 +276,8 @@ export const OrganizationSettingsPageView: FC<
 								</Button>
 							</div>
 						</div>
-					</HorizontalSection>
-				</HorizontalContainer>
+					</FormSection>
+				</HorizontalForm>
 			)}
 
 			<DeleteDialog