[analyzer] refactor: access IPAMode through the accessor.
[analyzer] Replace "-analyzer-ipa" with "-analyzer-config ipa".

The idea is to eventually place all analyzer options under
"analyzer-config". In addition, this lays the ground for introduction of
a high-level analyzer mode option, which will influence the
default setting for IPAMode.
[analyzer] Add "-analyzer-config mode=[deep|shallow] ".

The idea is to introduce a higher level "user mode" option for
different use scenarios. For example, if one wants to run the analyzer
for a small project each time the code is built, they would use
the "shallow" mode.

The user mode option will influence the default settings for the
lower-level analyzer options. For now, this just influences the ipa
modes, but we plan to find more optimal settings for them.