Create additional test target for go modules in bp2build

For go modules with non-empty testSrcs, we will create an additional
go_test target. To build a standalone test executable, we need to
include the source files in the compilation unit. This will be done
using the `embed` attribute
1. For tests of go_library, this is straightforward. It will embed the
   go_library and "inherit" its .go files and deps
2. For tetss of go_binary, we need to create an additional go_source
   target since go_binary cannot be embedded inside a go_test

Using `b test` for these tests revealed that certain tests are not
hermitic and rely on `testdata` files checked into the tree. This CL
introduces an allowlist to skip generating go_test targets for them.

Test: bp2build unit test
Test: TH
Bug: 284483729
Bug: 288491147
Change-Id: Ic736d655babc2f6067e4da75384900b7b8bdc2ed