Add keep-alive functionality

[michaeltintiuc]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (npm run build) was run locally and any changes were pushed
• Lint (npm run lint) has passed locally and any fixes were made for failures

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other (please describe):

What is the current behavior?

There is no way to cache components using ion-vue-router due limitations imposed by Vue API which state that keep-alive should be a direct child of transition when used together.

Issue Number: N/A

What is the new behavior?

Allows usage of keep-alive as a property of ion-vue-router

Basic usage:

<ion-vue-router keep-alive />

Equates to:

<keep-alive>
  <router-view />
</keep-alive>

Passing props:
<ion-vue-router :keep-alive="{ include: 'SomeComponent' }" />

Equates to:

<keep-alive include="SomeComponent">
  <router-view />
</keep-alive>

Same as the original API you can pass string, string[] or RegExp to include and exclude properties.

RegExp:
<ion-vue-router :keep-alive="{ include: /Some/ }" />

Equates to:

<keep-alive :include="/Some/">
  <router-view />
</keep-alive>

Does this introduce a breaking change?

• Yes
• No

[Livijn]

This would be very good!

[Livijn]

@mhartington Lets merge this, shall we?

[ggirardi1]

Is this implementation already working?

[michaeltintiuc]

@guilhermeagirardi would appreciate you testing this feature here https://github.com/ModusCreateOrg/ionic-vue if building from source is a problem. Consider this PR an RFC, any feedback is highly valuable

[liamdebeasi]

Thanks for the PR! I am going to close this as this is for the old Ionic Vue code base.