Improve workspace metadata file access

The folder `.metadata\.plugins\org.eclipse.core.resources\.projects ` contains multiple super small files per project.
Saving and loading small files on windows is inefficient. It costs needless performance (and has a overhead on filesystem due to blocksize).
For example the ~1000 projects in platform workspace need multiple seconds to load (while splash screen is shown).
Startup time could be improved by loading those files in parallel (see https://github.com/eclipse-platform/eclipse.platform/pull/1219) but it would help much more to just store all that information in a single - per workspace - file.
Before i start such a PR i would like to know if there is any concern.
On platform workspace the total size of those files is <10MB and would easily fit into a single file that is completely loaded into memory all at once. I also checked our adopters workspace which shows similar statistics.

I would start with combining all `.markers` and `.location` files into a single such file for each type.