Support pre-populating caches (pre-parsing data structures etc.)

[danielocfb]

Currently we only populate caches as part of the symbolization (or inspection) process. However, it may be beneficial to add support for pre-populating caches, so that symbolization (or inspection...) can be as fast as possible, even on the first run. This is more of an advanced use case, but it could be useful in some setups.

A bit of a complication may be that for DWARF at least, parsing of data structures is on-demand. So we only cache data structures necessary to satisfy a specific request. But with pre-population there is no request. So presumably we'd need to parse everything. But I'd think that's fine.