fix(select): height changes when disabled
fix(select): height changes when disabled

- use the same approach for `md-select`'s disabled border background-position as `md-input`
- `md-select` inside of an `md-input-container` uses more `md-input` SCSS variables
  - this allows it to better match the layout and dimensions of other `md-input-container` elements
- add new `$select-border-width-default` SCSS variable

Fixes #11812

bluebirdtech/material,bluebirdtech/material,marekmicek/material,clshortfuse/material,bluebirdtech/material,oostmeijer/material,oostmeijer/material,clshortfuse/material,angular/material,angular/material,marekmicek/material,oostmeijer/material,angular/material,bluebirdtech/material,oostmeijer/material,marekmicek/material,clshortfuse/material,marekmicek/material,clshortfuse/material,angular/material