[TabLayout] Support gravity_fill with "auto" mode

Nobody has claimed this yet.

**Description:** Setting the `tabMode` to `auto` is the same as setting the `tabMode` to `scrollable`. Even if there are only 2 items, they will never act like `fixed` tabs.

**Expected behavior:**
Expected to act as in [the documentation](https://developer.android.com/reference/com/google/android/material/tabs/TabLayout.html#MODE_AUTO)
> Auto-sizing tabs behave like MODE_FIXED with GRAVITY_CENTER while the tabs fit within the TabLayout's content width. Fixed tabs have equal width, based on the widest tab label. Once the tabs outgrow the view's width, auto-sizing tabs behave like MODE_SCROLLABLE, allowing for a dynamic number of tabs without requiring additional layout logic.

**Source code:**
By adding `app:tabMode="auto"` to the `tab_layout` view in `component_tabs.xml` and running the Material Theme Builder, you can see that the tabs no longer take up the full width of the parent. This occurs regardless of whether the parent is a LinearLayout or ConstraintLayout.

In [`updateTabViewLayoutParams` in `TabLayout`](https://github.com/material-components/material-components-android/blob/master/lib/java/com/google/android/material/tabs/TabLayout.java#L1568), it sets the `tabView` layout params' width to `WRAP_CONTENT` if the mode is not `MODE_FIXED`, not sure if that's the issue.

**Android API version:**
Seen on API 29.

**Material Library version:**
Seen on alpha07, alpha09, and alpha10.

**Device:**
Seen on Pixel 3 emulator.

Start in lib/java/com/google/android/material/tabs/TabLayout.java at updateTabViewLayoutParams, then reproduce the behavior by setting app:tabMode="auto" in component_tabs.xml and running the Material Theme Builder. Compare the result with the documented MODE_AUTO behavior for two tabs in both LinearLayout and ConstraintLayout parents; done means fitting tabs behave like fixed tabs and overflowing tabs remain scrollable.

Written by the indexing model from the issue text.