Toggle x coordinate freeze in geometry creation mode

`X`

All hotkeys for Gmsh 4.1.4

General Go to previous time step	`←`
General Go to next time step	`→`
General Make previous view visible	`↑`
General Make next view visible	`↓`
General Reload geometry	`0`
General Reload full project	`Ctrl` + `0`
General Mesh lines	`1`
General Mesh lines	`F1`
General Mesh surfaces	`2`
General Mesh surfaces	`F2`
General Mesh volumes	`3`
General Mesh volumes	`F3`
General Toggle mouse selection ON/OFF	`Esc`
General End/accept selection in geometry creation mode	`E`
General Go to geometry module	`G`
General Go to mesh module	`M`
General Go to post-processing module	`P`
General Abort selection in geometry creation mode	`Q`
General Go to solver module	`S`
General Toggle x coordinate freeze in geometry creation mode	`X`
General Toggle y coordinate freeze in geometry creation mode	`Y`
General Toggle z coordinate freeze in geometry creation mode	`Z`
General Bring all windows to front	`↑ Shift` + `A`
General Show geometry options	`↑ Shift` + `G`
General Show mesh options	`↑ Shift` + `M`
General Show general options	`↑ Shift` + `O`
General Show post-processing options	`↑ Shift` + `P`
General Show solver options	`↑ Shift` + `S`
General Show post-processing view plugins	`↑ Shift` + `U`
General Show post-processing view options	`↑ Shift` + `W`
General Move only along x coordinate in geometry creation mode	`↑ Shift` + `X`
General Move only along y coordinate in geometry creation mode	`↑ Shift` + `Y`
General Move only along z coordinate in geometry creation mode	`↑ Shift` + `Z`
General Enable full mouse selection	`↑ Shift` + `Esc`
General Attach/detach menu	`Ctrl` + `D`
General Export project	`Ctrl` + `E`
General Enter full screen	`Ctrl` + `F`
General Show statistics window	`Ctrl` + `I`
General Save model options	`Ctrl` + `J`
General Show message console	`Ctrl` + `L`
General Minimize window	`Ctrl` + `M`
General Create new project file	`Ctrl` + `N`
General Open project file	`Ctrl` + `O`
General Quit	`Ctrl` + `Q`
General Rename project file	`Ctrl` + `R`
General Save mesh in default format	`Ctrl` + `S`
General Show clipping plane window	`↑ Shift` + `Ctrl` + `C`
General Show current options and workspace window	`↑ Shift` + `Ctrl` + `H`
General Save options as default	`↑ Shift` + `Ctrl` + `J`
General Show manipulator window	`↑ Shift` + `Ctrl` + `M`
General Show option window	`↑ Shift` + `Ctrl` + `N`
General Merge file(s)	`↑ Shift` + `Ctrl` + `O`
General Show plugin window	`↑ Shift` + `Ctrl` + `U`
General Show visibility window	`↑ Shift` + `Ctrl` + `V`
General Loop through axes modes	`Alt` + `A`
General Hide/show bounding boxes	`Alt` + `B`
General Loop through predefined color schemes	`Alt` + `C`
General Hide/Show element outlines for visible post-pro views	`Alt` + `E`
General Change redraw mode (fast/full)	`Alt` + `F`
General Hide/show all post-processing views	`Alt` + `H`
General Hide/show all post-processing view scales	`Alt` + `I`
General Hide/show geometry lines	`Alt` + `L`
General Toggle visibility of all mesh entities	`Alt` + `M`
General Hide/show all post-processing view annotations	`Alt` + `N`
General Change projection mode (orthographic/perspective)	`Alt` + `O`
General Hide/show geometry points	`Alt` + `P`
General Loop through range modes for visible post-pro views	`Alt` + `R`
General Hide/show geometry surfaces	`Alt` + `S`
General Loop through interval modes for visible post-pro views	`Alt` + `T`
General Hide/show geometry volumes	`Alt` + `V`
General Enable/disable all lighting	`Alt` + `W`
General Set X view	`Alt` + `X`
General Set Y view	`Alt` + `Y`
General Set Z view	`Alt` + `Z`
General Hide/show small axes	`Alt` + `↑ Shift` + `A`
General Hide/show mesh volume faces	`Alt` + `↑ Shift` + `B`
General Loop through predefined colormaps	`Alt` + `↑ Shift` + `C`
General Hide/show mesh surface faces	`Alt` + `↑ Shift` + `D`
General Hide/show mesh lines	`Alt` + `↑ Shift` + `L`
General Hide/show mesh points	`Alt` + `↑ Shift` + `P`
General Hide/show mesh surface edges	`Alt` + `↑ Shift` + `S`
General Same as Alt + T, but with numeric mode included	`Alt` + `↑ Shift` + `T`
General Hide/show mesh volume edges	`Alt` + `↑ Shift` + `V`
General Set -X view	`Alt` + `↑ Shift` + `X`
General Set -Y view	`Alt` + `↑ Shift` + `Y`
General Set -Z view	`Alt` + `↑ Shift` + `Z`