`include` grammars don't load within `captures`

Embedded grammars are not loaded from disk when inside a captures rule

If the embedded grammar was pre-loaded by another include in the same grammar
OR loaded via another grammar in another language in another file
then it works as expected

1. Don't open a file that loads the C grammar
2. Open a file with the following grammar loaded
3. notice no syntax highlighting. test(5);

1. Close the file
2. Reload VSCode
3. Open a C file
4. Reopen the file with the following grammar loaded
5. notice syntax highlighting now working

{
	"scopeName": "source.capture.load",
	"patterns": [
		{
			"match": ".+",
			"captures": { "0": { "patterns": [ { "include": "source.c" } ] } }
		}
	]
}

from my testing getExternalGrammar() is never run when directly inside captures

related:

• https://github.com/microsoft/vscode-textmate/issues/141
• https://github.com/microsoft/vscode-textmate/issues/173
• https://github.com/microsoft/vscode-textmate/issues/174

Start by tracing how includes nested directly inside a captures rule are resolved, focusing on the reported getExternalGrammar() entry point. Reproduce the issue with the provided TextMate grammar and a C grammar loaded in VS Code. Done means the embedded source.c grammar loads on first use and syntax highlighting works without preloading it elsewhere.