(MicrosoftDocsGH-9033) Add casing functions for PSReadLine 2.3.0

The change in PowerShell/PSReadLine#3365 added three new functions for
modifying the casing of text with PSReadLine. This change:

- Adds an entry for each new function in the "Basic editing functions"
  section of `about_PSReadLine_Functions.md`
- Resolves MicrosoftDocs#9033
- Resolves AB#4387

reference/7.3/PSReadLine/About/about_PSReadLine_Functions.md

@@ -133,6 +133,16 @@ the host so the prompt is evaluated again.
 - Vi insert mode: `<Ctrl+c>`
 - Vi command mode: `<Ctrl+c>`
 
+### CapitalizeWord
+
+> Added in PSReadLine 2.3.0
+
+Convert the first character of the next word to upper case and the remaining
+characters to lower case.
+
+- Cmd: `<Alt+c>`
+- Emacs: `<Escape,c>`
+
 ### Copy
 
 Copy selected region to the system clipboard. If no region is selected, copy
@@ -237,6 +247,15 @@ Delete the next word.
 
 - Vi command mode: `<d,w>`
 
+### DowncaseWord
+
+> Added in PSReadLine 2.3.0
+
+Convert the next word to lower case.
+
+- Cmd: `<Alt+l>`
+- Emacs: `<Escape,l>`
+
 ### ForwardDeleteInput
 
 Like KillLine - deletes text from the point to the end of the input, but
@@ -404,6 +423,15 @@ the cursor. The cleared text is placed in the kill-ring.
 
 - Emacs: `<Ctrl+w>`
 
+### UpcaseWord
+
+> Added in PSReadLine 2.3.0
+
+Convert the next word to upper case.
+
+- Cmd: `<Alt+u>`
+- Emacs: `<Escape,u>`
+
 ### ValidateAndAcceptLine
 
 Attempt to execute the current input. If the current input is incomplete (for