Problem:  Can't detect angular & mustache filetypes
Solution: Detect *.mustache as Mustache filetype;
          detect *.component.html as html.angular filetype

closes: vim/vim#13594

https://github.com/vim/vim/commit/7bed263c343c62129c5d8f51796895a28db1b312

assert() would not abort in release builds, meaning an OOM condition
would be undetected.

Problem:
`LanguageTree:for_each_tree` calls itself for child nodes, so when we
calls `for_each_tree` inside `for_each_tree`, this quickly leads to
exponential tree calls.

Solution:
Use `pairs(child:trees())` directly in this case, as we don't need the
extra callback for each children, this is already handled from the outer
`for_each_tree` call