Parser::ParseConfigFile returns Result<void>

ParseApexConfigs() uses Parser::ParseConfigFile() to parse .rc files in
the target apex. ParseConfigFile() returning bool (with logging on
error) doesn't propagate the error message back to the callers
(including apexd or PackageManager).

We'd better to migrate other Parse*() methods of Parser class to return
Result<T>. But this change focuses on plumbing error progagation for
APEX configs.

Bug: 238820991
Test: atest CtsInitTestCases
Change-Id: Ifad97635dbb53a70053ec73a7a5b7e742466daf6