[FR]: Support entry_points with output_dir = False

### What is the current behavior?

Currently when enabling either splitting or multiple entry-points then output_dir = True is enabled.

This is actually only necessary for the splitting case which will produce unpredictable output files, the multiple entry-point case will produce multiple files but those files will have predictable names based on the esbuild configuration.

### Describe the feature

Setting `entry_points` will correctly declare outputs for each of the bundled outputs and source maps etc and only switch to output directory declaration if splitting is enabled.

Start by tracing how the Bazel rule handles entry_points, splitting, and output_dir. Compare generated outputs and source maps for multiple entry points with and without splitting; done means predictable outputs are declared without forcing output_dir unless splitting is enabled.

Written by the indexing model from the issue text.