[tests] Rework TypeBuilderTest SetUp/TearDown
- Create a unique temporary directory for each test in TypeBuilderTest and delete
it on TearDown.
- Change tests to use tempDir instead of Path.GetTempPath ()
- Change IsSerializable () test to how it was 11 years ago and have it write to a
file with a simple name (but now in a directory where noone else is writing)
- Change FieldsWithSameName (), FieldsWithSameNameAndType () and
MethodsWithSameNameAndSig () to use the default temp assembly (now in a
unique tempDir) instead of using the CreateTempAssembly ()
- Remove CreateTempAssembly function. It is dead code.