Add focus and blur support to InputNumber

[delesseps]

Useful for focusing the first field in a form which in this case may be an InputNumber

<InputNumber ref={(input) => this.amountInput = input} />

then inside lifecycle method like componentDidUpdate

this.amountInput.focus()

Brings into line with Input.focus

Related to PR 7577 against Master

[codecov]

Codecov Report

Merging #7615 into antd-3.0 will decrease coverage by 0.07%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##           antd-3.0    #7615      +/-   ##
============================================
- Coverage     82.14%   82.06%   -0.08%     
============================================
  Files           214      214              
  Lines          4441     4445       +4     
  Branches       1337     1337              
============================================
  Hits           3648     3648              
- Misses          793      797       +4

Impacted Files	Coverage Δ
components/input-number/index.tsx	70.58% <ø> (-21.72%)	⬇️

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