`WorkspaceBrowseConfiguration` should support multiple sets of compiler path/args

If I understand correctly, it’s not uncommon for CMake projects to consist of several subprojects that could use different relevant args or hypothetically even different compilers (i.e. target binaries vs. tools built for the host system to be used by the build).

There is also the need for C vs. C++ information, as compiler queries for either may result in different system include paths.

Processing N sets of compiler paths/args here would be similar to what cpptools does with compile_commands.json files - processes all provided compiler paths and (unique and relevant combinations of) args, to build the browse path(s). Cpptools should be able to avoid redundantly querying compilers, so it should not be critical that the configuration provider de-dupe this set.

Start by reading the WorkspaceBrowseConfiguration API and reviewing how cpptools processes compile_commands.json, as described in the issue. Define and document support for multiple compiler path/argument sets, including distinct C and C++ queries; done means the API can represent these sets for subprojects without requiring redundant compiler queries.