[clang-installapi] Store dylib attributes in the order they are passed on the command line. (#139087)
With the introduction of tbd-v5 holding rpaths, the order in which those
attributes are passed to `clang-installapi` must be represented in tbd
files. Previously, all dylib attributes were stored in a
non-deterministic `StringMap`. Instead, hold them in a custom collection
with an underlying vector to continue supporting searching by attribute.
This makes the order of all diagnostics related to load command
comparisons stable.
This approach resolves errors when building with reverse-iteration.