UI / Interface Navigation Issue

**Describe the bug**
Assets selection and max button cannot be selected or navigated to by using the keyboard tab key.

**Steps to reproduce (REQUIRED)**
Steps to reproduce the behaviour, libraries used with version number, and/or any setup information to easily reproduce:

1. Go to meta-mask extension and open it
2. Click on send and add recipient
3. Use tab key to navigate-> enter amount highlighted "skipping select assets drop dwon and max button"

**Expected behaviour**
Meta-mask opens, recipient added. Clicked tab key- assets drop down is highlighted. Used enter key to display drop down, used navigation keys to select desired asset and confirmed section using enter key.

Again pressed tab key and max button highlighted, clicked enter key to activate max value to display in the amount column.

**Screenshots**
Reference video attached- using cursor motion to highlight affected region.

https://user-images.githubusercontent.com/84296795/118420820-63017680-b6dd-11eb-9bfe-082ffaa8619c.mp4

**Browser details:**
- OS: [ Ubuntu]
- Browser: [Brave 64 bit- V 1.22.70 ]
- Meta-mask Version: [V 9.5.2]

**Additional context**
Mentioned issue fix could help those who rely entirely on keyboard to interact with apps or functions.

Start by reproducing the issue in the MetaMask extension's Send flow on Ubuntu with Brave, using only the Tab, Enter, and arrow keys. Inspect the implementation of the recipient, asset selector, amount, and Max controls; done means the asset selector and Max button receive focus in order and can be operated entirely from the keyboard.

Written by the indexing model from the issue text.