fix(treesitter): indent size for inspect_tree

[wookayin]

Problem: For :InspectTree, the tree viewer buffer with the filetype
query does not explicitly set the tab size, which can mismatch with
the indent size assumed by the TSTreeView implementation (default: 2).

Solution: Set shiftwidth to be the same as TSTreeViewOpts, which
defaults to 2.

[wookayin]

Before (with some indent-line plugin) when user's global &shiftwidth = 4:

After: vim.bo.shiftwidth is now 2.

Remark: we could instead set the default indent size for &ft = query (runtime/query.lua), but I chose to configure buffer-local settings because treeview.opts may have a different indent size set on-the-fly other than 2, according to the current implementation.

[zeertzjq]

I don't think 'tabstop' should be changed, as there are no Tabs in the text. But maybe 'expandtab' is needed?

[wookayin]

Forgot to mention that tabstop, etc. are for the query editor rather than InspectTree. For InspectTree right, we don't have tabs --- but the default options for query editors will be noexpandtab and tabsize=8. I thus have added the expandtab option in set_dev_properties.

[clason]

Let's leave the query editor for now; the plan is to include the formatter from nvim-treesitter for query files (including the editor).

[justinmk]

I don't think this needs to block 0.10

[clason]

@wookayin During feature freeze, we (only) use the milestone for actual blockers in order to manage the release process. Obviously this can and will be backported after the 0.10 release (and we can re-use the milestone for 0.10.x then).