set_query_var should have a helpful inline doc description

[webdevmattcrom]

set_query_var() does not have any description to help developers understand the purpose and/or context of this function. Adding inline docs will also help ensure the DevHub is accurate.

See here: https://core.trac.wordpress.org/browser/tags/4.9/src/wp-includes/query.php#L73

Suggested Description:
"set_query_var is a wrapper function to the global $wp_query that uses the method set."

[webdevmattcrom]

Patch for ticket #42783 -- adds inline doc per suggestion

[noisysocks]

In 49094:

Docs: Improve set_query_var() inline docs.

Makes the inline docs for set_query_var() consistent with the inline docs for
get_query_var().

See #42783.
Props stevenlinx, markparnell.

[SergeyBiryukov]

In 49095:

Docs: Synchronize descriptions of some query functions and their counterpart methods in WP and WP_Query classes:

• set_query_var()
• get_query_var()
• get_queried_object()
• get_queried_object_id()

Switch to third-person singular verbs, per the documentation standards.

See #50768, #42783.