feat: validate manifests

[mshanemc]

What does this PR do?

validate manifests are valid xml

What issues does this PR fix or reference?

@W-13505922@

Functionality Before

successfully wrote package.xml (but ignored invalid types)

Functionality After

Error (1): Invalid manifest file: package.xml.
InvalidTag Tag '<types' is an invalid name. (Line 3 Column 12)

[iowillhoit]

QA NOTES

• 🟢 Convert warns of invalid manifest <<types>
• 🟢 Convert warns of invalid manifest <types>>
• 🟡 Oddly this is valid xml? ><types>? No warning and everything converts correctly 🤷
  • So is <types>>?
• 🟢 Considers xml comments valid <members>FileUtilities<!-- comment --></members>
• 🟢 Considers extra newlines valid

</types>

    <version>57.0</version>
</Package>

• 🟢 project deploy start -x package.xml warns of invalid manifest
• 🟢 project retrieve start -x package.xml warns of invalid manifest
• 🟢 Nice message about missing a closing tag InvalidTag: Expected closing tag 'types
• 🟢 Convert, deploy, and retrieve all still work as expected with valid xml