### Context
By default, Objective-C code will only perform availability checks for iOS APIs introduced from iOS 11 and up. We can enable -Wunguarded-availability to turn on available checks for older SDKs.
Additional context for this behavior comes from [llvm](https://reviews.llvm.org/D34264);
> [This patch](https://reviews.llvm.org/D34264) adds a new warning flag called -Wunguarded-availability-new. If -Wunguarded-availability is off, this warning only warns about uses of APIs that have been introduced in macOS >= 10.13, iOS >= 11, watchOS >= 4 and tvOS >= 11. This warning is on by default. We decided to use this kind of solution as we didn't want to turn on -Wunguarded-availability by default, as we didn't want our users to get warnings about uses of old APIs in their existing projects.
### What's happening in this change
This change turns on -Wunguarded-availability. This has the effect of the compiler performing availability checks for all APIs at or above the current deployment target (iOS 8.0). As such, this PR addresses several instances of code that were not performing availability checks.
Going forward, we will be able to use availability to encode our supported SDKs into the APIs that we provide. For example, we could annotate MDCActivityIndicator with NS_AVAILABLE_IOS(9_0) and all of our code would then have to use runtime checks prior to using this API.
### Caveats
Because -Wunguarded-availability is not enabled by default in Objective-C, our clients will need to proactively enable this flag in order to be warned of any use of APIs that support OS versions < 11.0. We can mitigate this risk in two ways:
1. Clearly announce any changes in our supported OS versions.
2. Encourage clients to enable -Wunguarded-availability.
Removes the need to copy-paste stanzas from other files anymore as we'll rely on #4478 to generate the correct stanza for us instead.
This was an automated change generated by running a find-and-replace regular expression:
```
/\*
Copyright ([0-9]+)-present the Material Components for iOS authors\. All Rights Reserved\.
Licensed under the Apache License, Version 2\.0 \(the "License"\);
you may not use this file except in compliance with the License\.
You may obtain a copy of the License at
http://www\.apache\.org/licenses/LICENSE-2\.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied\.
See the License for the specific language governing permissions and
limitations under the License\.
\*/
```
```
/\*
Copyright ([0-9]+)-present the Material Components for iOS authors\. All Rights Reserved\.
Licensed under the Apache License, Version 2\.0 \(the "License"\);
you may not use this file except in compliance with the License\.
You may obtain a copy of the License at
http://www\.apache\.org/licenses/LICENSE-2\.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied\.
See the License for the specific language governing permissions and
limitations under the License\.
\*/
```
```
/\*
Copyright ([0-9]+)-present the Material Components for iOS authors\. All Rights Reserved\.
Licensed under the Apache License, Version 2\.0 \(the "License"\);
you may not use this file except in compliance with the License\.
You may obtain a copy of the License at
http://www\.apache\.org/licenses/LICENSE-2\.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied\.
See the License for the specific language governing permissions and
limitations under the License\.
\*/
```
```
// Copyright $1-present the Material Components for iOS authors. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
```
* [Typography] Add TypographyScheme example
The new Typography Scheme as missing examples and the old Typography examples
did not have sufficient contrast ratios for AA-level accessible text.
Internal: b/77907063
* Reducing section divider opacity
All examples now have at least the required `+catalogBreadcrumbs` and `+catalogIsPrimaryDemo`. All examples in the same breadcrumbs path have only one primary demo. There should be only one `-catalogDescription` attached to the primary demo.
Closes#1897
