Upgrade to Docsy 0.5.1

[chalin]

• We'll be building upon the successful integration of: Bump Docsy to 0.3.x #48721
• This is a step of Should update theme/docsy step by step to the latest docsy  #44002
• Partly contributes to Align with upstream Docsy #41171
• Upgrade to 0.5.1 from 0.3.0, because 0.5.1 is the first official version that supports use of Docsy via an NPM module.

Issues found and to be resolved in scope of this work:

• Bootstrap and Font Awesome (as part of Docsy) are deprecated #32905
• There are two <script> elements referencing jQuery #48806
• Named code-block elements show unnecessary block padding #48808
• Use canonical FontAwesome v6 icon names, upgrading from v3-v5 #48811. Actually, all v3-v5 IDs should be updated to use the v6 icon's canonical name
• Tab panes have formatting issues #48813

Note that @sftim did some preliminary exploration:

• Bump Docsy to 0.4.x #48722
• Bump Docsy to 0.5.x #48723
• Etc

Resources:

• Changelog#v0.5.1
• google/docsy@v0.3.0...v0.5.1

/assign
/cc @nate-double-u

[sftim]

/area web-development
/triage accepted