feat(scalable content): add code snippets

[juchengchou]

Refer to go/ptz-compose-snippets-wip we put the code onto github then we can use them for new DAC page.

[snippet-bot]

Here is the summary of changes.

You are about to add 3 region tags.

• compose/snippets/src/main/java/com/example/compose/snippets/accessibility/ScalableContentSnippets.kt:57, tag android_compose_accessibility_scalable_content_density_scaling
• compose/snippets/src/main/java/com/example/compose/snippets/accessibility/ScalableContentSnippets.kt:101, tag android_compose_accessibility_scalable_content_font_scaling
• compose/snippets/src/main/java/com/example/compose/snippets/accessibility/ScalableContentSnippets.kt:144, tag android_compose_accessibility_scalable_content_demo_card

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[khufdev]

Added one suggestion related to comments -- also, make the necessary fixes so that the build succeeds.