Fix the JS test shard dropping results and never awaiting the snapshot tests [CLF-454]

[zach-klippenstein]

The "JS Unit Tests for KMP Modules" shard has not been testing what it claims to. Two independent problems, both present on main:

1. Gradle throws away most of the Karma results

KGP's Karma reporter (kotlin-web-helpers/dist/karma-kotlin-reporter.js) writes its ##teamcity[...] service messages to stdout back-to-back with no newline between them. KGP's Gradle-side parser (TCServiceMessageOutputStreamHandler) buffers stdout until it sees a newline and drops any "line" longer than 1 MiB, logging:

Cannot process output: too long teamcity service message (more than 1Mb). Event was lost.
java.lang.IllegalStateException: no running test

Since the whole run is a single line, every 1 MiB chunk is discarded and only the final remainder is parsed. On recent main runs Gradle recorded roughly 2,000 of the 27,955 workflow-runtime JS tests that actually run. Any failure inside a dropped chunk is invisible, so the shard is green regardless.

Fix: build-logic/karma.config.d/newline-delimited-kotlin-reporter.js wraps KGP's reporter so every message ends with a newline, and KotlinMultiPlatformConventionPlugin appends that directory to every generated karma.conf.js via KotlinKarma.useConfigDirectory. After this change all 27,955 workflow-runtime and 50 workflow-core tests are recorded and the overflow message is gone.

2. Burst never awaits RenderWorkflowInSnapshotSaveRestoreTest on JS

Burst 2.13.0 only generates specializations that return runTest(...) { … } when the parameterized test function's body calls runTest itself. When runTest is behind a helper (which #1568 introduced to dodge a Kotlin/Native compiler crash), the generated per-value functions call the original as a bare statement and return nothing. On JS that return value is the Promise Mocha has to await, so all 4,096 saves_to_and_restores_from_snapshot_* tests completed instantly and "passed" without their bodies ever finishing. Those thousands of un-awaited bodies then ran concurrently with the rest of the suite and starved the event loop, which is what made unrelated tests hit Mocha's 2 s timeout on #1442.

Fix: the test calls runTest directly again, but with no arguments that reference this (the shape that crashes Kotlin/Native), and launches both runtimes in explicit TestScope(dispatcherUsed) scopes instead. The class KDoc documents both constraints. Burst itself should also be fixed to return the delegate's value; that's a follow-up.

Verification

Locally, with these changes on main:

Task	Recorded	Failures
:workflow-runtime:jvmTest (this class)	16,384	0
:workflow-runtime:iosSimulatorArm64Test (this class)	16,384	0
:workflow-runtime:jsBrowserTest (full)	27,955	0
:workflow-core:jsBrowserTest (full)	50	0

Ref: CLF-454

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