Improve initialization speed of extension

[pluyckx]

Describe the solution you'd like
Speed up the initialization time needed for this extension. Using some kind of cache that stores which IAR workbenches are installed with their default defines/includes will help. This will not change as long as no updates are installed for that workbench.

The minimum data that should be stored in the cache:

• IAR workbench/compiler location
• default defines
• default includes
• last time the compiler/workbench was changed (to detect updates and thus to detect when to update default defines/includes)

The cache can be stored in the extension folder (and not in the workspace folder). This data is useful for all workspaces.

Additional context
When a lot of workbenches are installed (and especially old versions), it can take some time to initialize the extension.