docs(material/expansion-panel): accordion example throws No provider found for DateAdapter

[h3d0]

Bug

Detailed Reproduction Steps:

1. Go to https://material.angular.io/components/expansion/examples
2. Open Dev Console

What is the expected behavior?

Accordion example is working.

What is the current behavior?

Accordion example is broken:

What is the use-case or motivation for changing an existing behavior?

All users visiting a website are affected.

Which versions of AngularJS, Material, OS, and browsers are affected?

• AngularJS: 9.1.0
• AngularJS Material: 9.1.0
• OS: All
• Browsers: All

[Splaktar]

Please submit Angular Material and CDK questions here and issues here. This repo is for AngularJS Material.

I have transferred this issue to the correct repository for you.

[Splaktar]

I beleive that this is due to

components/src/components-examples/material/expansion/index.ts

Lines 26 to 32 in 6baffb3

	imports: [
	MatButtonModule,
	MatDatepickerModule,
	MatExpansionModule,
	MatIconModule,
	MatInputModule,
	],

not importing a DateAdapter.