This character is a Other Symbol and is commonly used, that is, in no specific script. The character is also known as shift and level 2 select (ISO 9995-7).
The glyph is not a composition. Its width in East Asian texts is determined by its context. It can be displayed wide or narrow. In bidirectional text it acts as Other Neutral. When changing direction it is not mirrored. The word that U+21E7 forms with similar adjacent characters prevents a line break inside it.
The CLDR project calls this character “upwards hollow arrow” for use in screen reading software.
The Wikipedia has the following information about this codepoint:
The Shift key⇧ Shift is a modifier key on a keyboard, used to type capital letters and other alternate "upper" characters. There are typically two shift keys, on the left and right sides of the row below the home row. The Shift key's name originated from the typewriter, where one had to press and hold the button to shift up the case stamp to change to capital letters;
the shift key was first used in the Remington No. 2 Type-Writer of 1878; the No. 1 model was capital-only.
On the US layout and similar keyboard layouts, characters that typically require the use of the shift key include the parentheses, the question mark, the exclamation point, and the colon.
When the caps lock key is engaged, the shift key may be used to type lowercase letters on many operating systems, though not on macOS.