fix: Merging does not work if original report folders contain only index.html

Fixes #7
Thank you @QuaidBartolomei for the fix

• Creates the output path if it does not exist

fix: copy issues, compile target, trace app, add overwrite and debug option

Merges - #6
Thank you @nickofthyme

This adds the following:

• Set transpilation target to node12
• Copies the trace/ app to the final merged report only if any of the original reports contain it. All trace .zip test files were already being copied correctly.
• Adds debug option to allow user to control verbosity. (default: false)
• Adds overwriteExisting option to control overwriting existing report. (default: true)
• Fixes error with contentFolderPath when copying data/, it was not joining the src and filename path correctly. See code line diff here.

Report merge fixes

Merged - #5
Thank you @nickofthyme

• Issue with merging the base64 encoded data/ files across many reports including those within the same test suite. This included merging the running stats.
• Issue with merging reports with no failures, hence no data/ files.
• Issue with finding the index.html file from playwright-core. This appears to have been fixed #3 but I think a better approach is just to use the index.html file that we already have while merging the reports.

Timing issue writing index.html content

Thank you @nickofthyme for the #2 fix.

The correct files/assets were in the original two reports and all the correct files/assets were in the final merge report. However, digging deeper, I noticed that the index.html file was missing content in the base64 zip content.

Resolve module issue and missing data folder

Thank you @mrmckeb for #3 .

Fixes

• The data folder may not be present if no screenshots or traces were captured.
• playwright-core may not exist in the specified location. Instead, this package will now find playwright-core directly.