Add glyphs for `lrm`, `rlm`, and `space.nobreak.narrow` in the General Symbols page

[MDLC01]

Description

Most space characters and other non-printable characters have a glyph in the General Symbols page, in the form of a short name or corresponding symbol (e.g., "␣" for space, "nbsp" for space.nobreak, or "wjoin" for wj). I suggest adding similar glyphs for lrm (probably "lrm"), rlm (probably "rlm"), and space.nobreak.narrow (probably "nnbsp").

Use Case

Making the symbol list more consistent and slightly easier to read.