Styles: move $icon-nav-link-padding-y and $icon-nav-link-padding-x to variables.scss

[why520crazy]

We are removed all secondary styles import entries in next version 13 such as:

// it is ok in preview versions, but is not ok in 13
@use "ngx-tethys/nav/styles/icon-nav.scss" as icon-nav;

.xxx {
 padding: icon-nav.$icon-nav-link-padding-x;
}

Need support new ways to use it:

@use "ngx-tethys/styles/variables.scss" as variables;

.xxx {
 padding: variables.$icon-nav-link-padding-x;
}

or

@use "ngx-tethys/styles/basic.scss" as basic;

.xxx {
 padding: basic.$icon-nav-link-padding-x;
}