Add zIndex prop to renderToLayer HOC

[chenesan]

Purpose

To enable adjusting zIndex of base layer of <Popup /> or <Popover />, added zIndex prop on renderToLayer HOC.

Changes

• a list of what have been done
• maybe some code change

Risk

Usually none, if you have any please write it here.

TODOs

• Describe what should be done outside of this PR
• Maybe in other PRs or some manual actions.

[sonarcloud]

Kudos, SonarCloud Quality Gate passed!   

0 Bugs
0 Vulnerabilities
0 Security Hotspots
0 Code Smells

No Coverage information
0.0% Duplication

[codecov]

Codecov Report

Merging #409 (8dc8de2) into develop (b9d0b0e) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@             Coverage Diff             @@
##           develop     #409      +/-   ##
===========================================
+ Coverage    88.43%   88.45%   +0.02%     
===========================================
  Files          151      151              
  Lines         1539     1542       +3     
  Branches       281      283       +2     
===========================================
+ Hits          1361     1364       +3     
  Misses         178      178              

Files Changed	Coverage Δ
packages/core/src/mixins/renderToLayer.js	100.00% <100.00%> (ø)