Small out-of-tree extension fixes/features

[samansmink]

This PR introduces some changes that I need to nicely refactor the sqlite_scanner extension in PR: duckdb/sqlite_scanner#56

• Fixes extension name -> extension class name conversion (now properly converts snake case to camel case)
• Change edge case handling for original sqlite tests: these break things in my sqlite_scanner extension refactoring, now the pattern match is a bit more specific
• Allow running SQLLogicTests with require <ext name> to load loadable extension instead to be able to test extensions that can not be statically linked from CI

These changes allow running tests for extensions that are not statically linked. So consider the extension config:

duckdb_extension_load(aws
    LOAD_TESTS
    DONT_LINK
    GIT_URL https://github.com/duckdblabs/duckdb_aws
    GIT_TAG 617a4b1456eec1dee3d668f9ce005a1de9ef21c8
)

When building, all tests from https://github.com/duckdblabs/duckdb_aws/tests/sql will be loaded, and the require aws in sqllogictests will perform a `LOAD '/build//extensions/aws/aws.duckdb_extension' instead of trying to load the statically linked extension.

The reason this is added is the fact that the sqlite scanner cannot be linked on windows due to symbol collision with, but we still want to run its tests from duckdb's CI.