Since Karma with Bazel does not support ESM natively, we bundle the
tests using ESBuild into a single AMD file. This not only solves the
ESM issue until we can run browser ESM tests natively (also pending
in the components repo - the esbuild generation follows ESM semantics
but since collapsed we don't rely on the real module system).
A benefit of bundling is also faster and more reliable Karma browser
tests since only a single file needs to be loaded- compared to hundreds
of individual files.
PR Close#48521
