Update tabs to reflect the material design bottom navigation spec:
https://material.google.com/components/bottom-navigation.html#bottom-nav
igation-usage
BREAKING CHANGES:
Material design mode defaults have changed to the following:
```
tabsHighlight: false,
tabsPlacement: 'bottom',
tabsHideOnSubPages: false
```
`tabsHighlight` can now be passed as an attribute on the `ion-tabs`
element, this allows for tabs to be added in multiple places inside of
an app and enable the highlight on some of them.
references #7455
Use NavController as the public API, and NavControllerBase as the
internal API. Refactored all app/nav/tabs unit tests and created
centralized mocking functions.
The input highlight can now be enabled for ios. Fixed wp’s
valid/invalid highlighting. The highlight bar now goes on top of the
item-inner border so it will resize if there is an icon to the left.
BREAKING CHANGES:
Fixed typos in the input highlight variables:
- `$text-input-md-hightlight-color-valid` ->
`$text-input-md-highlight-color-valid`
- `$text-input-wp-hightlight-color-valid` ->
`$text-input-wp-highlight-color-valid`
Modified variables to turn on/off the highlight:
ios (defaults to false for all):
```
$text-input-ios-show-focus-highlight: false !default;
$text-input-ios-show-valid-highlight:
$text-input-ios-show-focus-highlight !default;
$text-input-ios-show-invalid-highlight:
$text-input-ios-show-focus-highlight !default;
```
md (defaults to true for all):
```
$text-input-md-show-focus-highlight: true !default;
$text-input-md-show-valid-highlight:
$text-input-md-show-focus-highlight !default;
$text-input-md-show-invalid-highlight:
$text-input-md-show-focus-highlight !default;
```
wp (defaults to true for all):
```
$text-input-wp-show-focus-highlight: true !default;
$text-input-wp-show-valid-highlight:
$text-input-wp-show-focus-highlight !default;
$text-input-wp-show-invalid-highlight:
$text-input-wp-show-focus-highlight !default;
```
fixes#6449
references #5052
The Material Design spec has added “Bottom Navigation”, which is what
Ionic calls “Tabs”. Ionic’s MD mode now follows the updated Material
Design spec with the tabbar placed on the bottom. Additionally, any tab
sub pages do not automatically cover up the tabbar. Covering up the
tabbar is still possible by using a modal, however, it is no longer a
default feature for MD mode.
