count dynamic cross-chunk imports as dependencies

[evanw]

The hash included in the file name of each output file is intended to change if and only if anything relevant to the content of that output file changes. It includes:

• The contents of the file with the paths of other output files omitted
• The output path of the file the final hash omitted
• Some information about the input files involved in that output file
• The contents of the associated source map, if there is one
• All of the information above for all transitive dependencies found by following import statements

However, this didn't include dynamic import() expressions due to an oversight. With this release, dynamic import() expressions are now also counted as transitive dependencies. This fixes an issue where the content of an output file could change without its hash also changing. As a side effect of this change, dynamic imports inside output files of other output files are now listed in the metadata file if the metafile setting is enabled.

Fixes #1076