twister: Fields for Kconfig and DT overlay files in testcase.yaml

This is an implementation of issue #48334 and adds support for
specifying additional config and device tree overlays through fields in
the testcase.yaml file, which is more readable than having to cram these
in to `extra_args`.

Consider this example which shows the original and new ways to add
config and DT overlays:

```
common:
  extra_args: "CONF_FILE=a.conf;b.conf
DTC_OVERLAY_FILE=w.overlay;x.overlay OVERLAY_CONFIG=e.conf
UNRELATED=abc"
tests:
  utilities.base64:
    extra_conf_files:
      - "c.conf"
      - "d.conf"
    extra_overlay_confs:
      - "extra_overlay.conf"
    extra_dtc_overlay_files:
      - "y.overlay"
      - "z.overlay"
    extra_configs:
      - CONFIG_SAMPLE=y
    tags: base64
    type: unit
```

The new fields are `extra_conf_files`, `extra_overlay_confs,
`extra_dtc_overlay_files`. Files specified in these sections are appended
to any `CONF_FILE`, `OVERLAY_CONFIG`, or `DTC_OVERLAY_FILE` fields in
`extra_args`, causing the following args being passed in to
`self.run_cmake` at `runner.py:850`:

```
['-DUNRELATED=abc',
 '-DCONF_FILE=a.conf;b.conf;c.conf;d.conf',
 '-DDTC_OVERLAY_FILE=w.overlay;x.overlay;y.overlay;z.overlay',
 '-DOVERLAY_CONFIG=e.conf extra_overlay.conf '
 '<build_dir>/twister/testsuite_extra.conf']
```

These fields can be used in the common or scenario-specific YAML
sections and will be merged in order of least to most specific:

 1. config files extracted from common's extra_args
 2. files listed in common's {extra_conf_files or extra_overlay_confs
    or extra_dtc_overlay_files}
 3. config files extracted from test scenario's extra_args
 4. files listed in test scenario's {extra_conf_files or
    extra_overlay_confs or extra_dtc_overlay_files}

Specifying these files in extra_args now triggers a deprecation warning,
as the direct YAML fields are preferred for readability. They will still
function for now but support will be dropped in the future.  One
testcase.yaml
(`zephyr/tests/cmake/overlays/var_expansions/testcase.yaml`) is
converted to use the new fields. A follow-up PR will convert the
remaining files to the new format.

Signed-off-by: Tristan Honscheid <honscheid@google.com>

scripts/schemas/twister/testsuite-schema.yaml

@@ -32,6 +32,21 @@ mapping:
       "extra_args":
         type: str
         required: false
+      "extra_conf_files":
+        type: seq
+        required: false
+        sequence:
+          - type: str
+      "extra_overlay_confs":
+        type: seq
+        required: false
+        sequence:
+          - type: str
+      "extra_dtc_overlay_files":
+        type: seq
+        required: false
+        sequence:
+          - type: str
       "extra_sections":
         type: str
         required: false
@@ -201,6 +216,21 @@ mapping:
             required: false
             sequence:
               - type: str
+          "extra_conf_files":
+            type: seq
+            required: false
+            sequence:
+              - type: str
+          "extra_overlay_confs":
+            type: seq
+            required: false
+            sequence:
+              - type: str
+          "extra_dtc_overlay_files":
+            type: seq
+            required: false
+            sequence:
+              - type: str
           "extra_sections":
             type: str
             required: false