Upgrade to istanbul-api

[riptl]

Pull request checklist

• All tests pass. Demo project builds and runs.
• I have resolved any merge conflicts.

What's in this pull request?

Replace istanbul (deprecated) with istanbul-api in package.json

Why?

gulpfile.js depends on istanbul-api, but currently only istanbul is imported.

core-js/gulpfile.js

Line 7 in bbbc406

const istanbul = require('istanbul-api');

core-js/package.json

Line 101 in bbbc406

"istanbul": "^1.1.0-alpha.1",

As a result, the build fails with package managers without flat node_modules (such as pnpm.js.org)

[codecov]

Codecov Report

Merging #496 into master will increase coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master     #496      +/-   ##
==========================================
+ Coverage   70.39%   70.43%   +0.03%     
==========================================
  Files         201      201              
  Lines       12530    12530              
==========================================
+ Hits         8820     8825       +5     
+ Misses       3710     3705       -5

Impacted Files	Coverage Δ
.../main/generic/consensus/full/FullConsensusAgent.js	58.91% <0%> (+0.49%)	⬆️
src/main/generic/consensus/InvRequestManager.js	81.08% <0%> (+10.81%)	⬆️

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