fix(lambda-python): asset files are generated inside the 'asset-input' folder (aws#18306)

Changes the asset structure from:

```
├── asset.993168cfa75b295eeea55bf603340284b9be46ebc079e4965f2c16f5470efda5
│   └── asset-input
│       ├── __init__.py
│       └── app.py
```

to:

```
├── asset.993168cfa75b295eeea55bf603340284b9be46ebc079e4965f2c16f5470efda5
│   ├── __init__.py
│   └── app.py
```

Fixes aws#18301.

----

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Author: otaviomacedo

Diff for: packages/@aws-cdk/aws-lambda-python/lib/bundling.ts

@@ -86,8 +86,8 @@ export class Bundling implements CdkBundlingOptions {
     bundlingCommands.push(packaging.exportCommand ?? '');
     if (packaging.dependenciesFile) {
       bundlingCommands.push(`python -m pip install -r ${DependenciesFile.PIP} -t ${options.outputDir}`);
-    };
-    bundlingCommands.push(`cp -R ${options.inputDir} ${options.outputDir}`);
+    }
+    bundlingCommands.push(`cp -R ${options.inputDir}/ ${options.outputDir}`);
     return bundlingCommands;
   }
 }

Diff for: packages/@aws-cdk/aws-lambda-python/test/bundling.test.ts

@@ -36,7 +36,7 @@ test('Bundling a function without dependencies', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'cp -R /asset-input /asset-output',
+        'cp -R /asset-input/ /asset-output',
       ],
     }),
   }));
@@ -62,7 +62,7 @@ test('Bundling a function with requirements.txt', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'python -m pip install -r requirements.txt -t /asset-output && cp -R /asset-input /asset-output',
+        'python -m pip install -r requirements.txt -t /asset-output && cp -R /asset-input/ /asset-output',
       ],
     }),
   }));
@@ -81,7 +81,7 @@ test('Bundling Python 2.7 with requirements.txt installed', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'python -m pip install -r requirements.txt -t /asset-output && cp -R /asset-input /asset-output',
+        'python -m pip install -r requirements.txt -t /asset-output && cp -R /asset-input/ /asset-output',
       ],
     }),
   }));
@@ -101,7 +101,7 @@ test('Bundling a layer with dependencies', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input /asset-output/python',
+        'python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input/ /asset-output/python',
       ],
     }),
   }));
@@ -121,7 +121,7 @@ test('Bundling a python code layer', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'cp -R /asset-input /asset-output/python',
+        'cp -R /asset-input/ /asset-output/python',
       ],
     }),
   }));
@@ -141,7 +141,7 @@ test('Bundling a function with pipenv dependencies', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'PIPENV_VENV_IN_PROJECT=1 pipenv lock -r > requirements.txt && rm -rf .venv && python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input /asset-output/python',
+        'PIPENV_VENV_IN_PROJECT=1 pipenv lock -r > requirements.txt && rm -rf .venv && python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input/ /asset-output/python',
       ],
     }),
   }));
@@ -161,7 +161,7 @@ test('Bundling a function with poetry dependencies', () => {
     bundling: expect.objectContaining({
       command: [
         'bash', '-c',
-        'poetry export --with-credentials --format requirements.txt --output requirements.txt && python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input /asset-output/python',
+        'poetry export --with-credentials --format requirements.txt --output requirements.txt && python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input/ /asset-output/python',
       ],
     }),
   }));
@@ -184,7 +184,7 @@ test('Bundling a function with custom bundling image', () => {
       image,
       command: [
         'bash', '-c',
-        'python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input /asset-output/python',
+        'python -m pip install -r requirements.txt -t /asset-output/python && cp -R /asset-input/ /asset-output/python',
       ],
     }),
   }));