CDRIVER-5866 Use consistent syntax for include directives

[eramongodb]

Resolves CDRIVER-5866 (comprehensive followup to #1836). Changes split from ongoing work on CDRIVER-5670.

Note

Sorting and grouping of include directives will still be addressed by CDRIVER-5670.

Consistently applies <>-syntax + library prefix to all include directives of all library headers.

The changes are applied using the following "rules":

• Library headers are included using the same syntax as users are expected to use.
  • Makes internal code depend on the "same" include directory paths as what is configured for users.
  • All system and third-party headers now also use <>-syntax.
• Test, example, and fuzzing components are excluded due to not yet being organized in prefix-friendly directories.
  • These are the only include directives still using ""-syntax.
  • Updated so the included header is always relative to the current file containing the directive.
  • No implicit dependence on include directory path configuration.

As a drive-by fix, updates the Jinja2 templates files to avoid inserting extra trailing newlines in the source files which may trigger git warnings of the form:

<stdin>:9: new blank line at EOF.
+
warning: 1 line adds whitespace errors.

[kevinAlbs]

LGTM. I support moving towards internal code that better resembles expected use.