fix(modal): Allow ModalScaffold to take no buttons

[soulcramer]

📋 Changes

Hide the Bottom App Bar in the Modal when no actions are provided and in the Dialog layout I've also added the Close action so we still have a clear way to indicate that the Dialog can be closed with an action.

A new example screen as been added for testing.

🤔 Context

I didn't expect from the specs that the Modal could have no actions. This is now clarified so we need to hide the Bottom App Bar when no actions are provided.

Closes #1168

✅ Checklist

• [x] I have reviewed the submitted code.
• [x] I have tested on a phone device/emulator.
• [x] If it includes design changes, please ask for a review spark-design GitHub team. @adevinta/spark-design

📝 Other Info

I've added a private api to be able to combine 2 PaddingValues between each others and we may want to publish it in the future if it's not planned by Google 🤔

[github-actions[bot]]

Job Summary for Gradle

👷 Build → 🧑‍🔬 Test → 🕵️ Lint :: validation

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
spark-android	dependencyGuard	8.7	:white_check_mark:
spark-android	spotlessCheck :build-logic:spotlessCheck	8.7	:x:

[soulcramer]

@spark-ui-bot spotless

[github-actions[bot]]

Job Summary for Gradle

👷 Build → 🧑‍🔬 Test → 🕵️ Lint :: dokka

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
spark-android	dokkaHtmlMultiModule	8.7	:x:

[github-actions[bot]]

Job Summary for Gradle

👷 Build → 🧑‍🔬 Test → 🕵️ Lint :: validation

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
spark-android	dependencyGuard	8.7	:white_check_mark:
spark-android	spotlessCheck :build-logic:spotlessCheck	8.7	:x:

[github-actions[bot]]

Job Summary for Gradle

👷 Build → 🧑‍🔬 Test → 🕵️ Lint :: validation

Gradle Root Project	Requested Tasks	Gradle Version	Build Outcome	Build Scan®
spark-android	dependencyGuard	8.7	:white_check_mark:
spark-android	spotlessCheck :build-logic:spotlessCheck	8.7	:x:

[soulcramer]

@spark-ui-bot spotless