STCLI-292 BREAKING prune babelConfig, stripes-testing

[zburke]

Summary

• update @folio/stripes-webpack from v7 to v8 (v8 no longer relies on babel-loader)
• remove the public export (previously, babelOptions from @folio/stripes-webpack was re-exported)
• replace babel-plugin-istanbul with istanbul-lib-instrument
• remove the @folio/stripes-testing dependency (nothing has relied on it since the NightmareJS tests were purged from platform-complete years ago and it's hard to believe we didn't think of doing this sooner)

Motivation

1. Most packages pull in @folio/stripes-webpack transitively, typically via this package. Thus, the way to supply the updated version of stripes-webpack is to update it here in stripes-cli. The changes here (removing babel-loader [by updating stripes-webpack] and @folio/stripes-testing) allow dependent libraries to substantially clean up their own dependency hierarchy by removing these two very old dependencies.
2. babelOptions was re-exported back in the BTOG days. Without babel-loader, we no longer have or need babelOptions.

Refs STCLI-292

[github-actions]

Jest Unit Test Results

0 tests  ±0   0 ✅ ±0   0s ⏱️ ±0s
0 suites ±0   0 💤 ±0 
0 files   ±0   0 ❌ ±0 

Results for commit 5402761. ± Comparison against base commit d30f7df.

♻️ This comment has been updated with latest results.

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
82.4% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[zburke]

@JohnC-80, I re-requested a review because two important changes were not yet in place when I asked you to look at this earlier (sorry):

1. actually remove the babelOptions export, i.e. the actual breaking change
2. replace babel-plugin-istanbul with istanbul-lib-instrument because (duh) it's not possible to use a babel-based coverage tool since stripes-webpack v8 no longer loads via babel 🤦 Prior to this change, yarn stripes test karma would fail given --coverage.