builtin: use api v2.0 and update dir structure (#49275)

* Bump the package API of the `builtin` repo to `v2.0`
* Move `var/spack/repos/builtin` -> `var/spack/repos/spack_repo/builtin`
* Move test repos `var/spack/repos/{builtin.mock,tutorial,...}` -> `var/spack/test_repos/`
* Update package dir names to v2 format (`-` -> `_` etc)
* Change absolute imports `from spack.pkg.builtin.my_pkg ...` to relative imports `from ..my_pkg.package ...`

Users who have a repo on top of builtin should change imports from

```python
from spack.pkg.builtin.my_pkg import MyPkg
```

to

```python
from spack_repo.builtin.packages.my_pkg.package import MyPkg
```

and can configure their editors with

```
PYTHONPATH=$spack/lib/spack:$spack/var/spack/repos
```

[skip-verify-checksums]

var/spack/repos/spack_repo/builtin/packages/blast2go/package.py

@@ -0,0 +1,48 @@
+# Copyright Spack Project Developers. See COPYRIGHT file for details.
+#
+# SPDX-License-Identifier: (Apache-2.0 OR MIT)
+
+import archspec
+
+from spack.package import *
+
+
+class Blast2go(Package):
+    """Blast2GO is a bioinformatics platform for high-quality functional
+    annotation and analysis of genomic datasets."""
+
+    homepage = "https://www.blast2go.com/"
+
+    version("5.2.5", sha256="c37aeda25f96ac0553b52da6b5af3167d50671ddbfb3b39bcb11afe5d0643891")
+
+    for t in set(
+        [str(x.family) for x in archspec.cpu.TARGETS.values() if str(x.family) != "x86_64"]
+    ):
+        conflicts("target={0}:".format(t), msg="blast2go is available x86_64 only")
+
+    depends_on("bash", type="build")
+    depends_on("blast-plus", type="run")
+    depends_on("java", type="build")
+
+    def url_for_version(self, version):
+        fname = "Blast2GO_unix_{0}.zip".format(version.underscored)
+        return "http://resources.biobam.com/software/blast2go/nico/%s" % fname
+
+    def install(self, spec, prefix):
+        # blast2go install script prompts for the following:
+        #
+        # continue? [o/c] => o
+        # installation prefix => prefix
+        # desktop icon [y/n] => n
+        # run blast2go? [y/n] => n
+
+        config_input_file = "spack-config.in"
+
+        config_input_data = ["o\n", prefix.bin + "\n", "n\n", "n\n"]
+
+        with open(config_input_file, "w") as f:
+            f.writelines(config_input_data)
+
+        with open(config_input_file, "r") as f:
+            bash = which("bash")
+            bash("Blast2GO_unix_%s.sh" % self.version.underscored, input=f)