Support syntax highlight for embedded SQL languages

[testforstephen]

When embedding SQL into the Java code, it will be helpful to show the syntax highlight for the SQL.

VS Code provides a guide about how to support embedded languages. https://code.visualstudio.com/api/language-extensions/syntax-highlight-guide#embedded-languages

There is a VS Code extension already providing SQL support.
0x00000001A/es6-string-html#10
https://marketplace.visualstudio.com/items?itemName=hjb2012.vscode-es6-string-html

[yaohaizh]

Add previous closed issue: #525

[fwgreen]

With Text Blocks coming in Java 13, this feature could have real utility. Maybe support for HTML should be considered as well.

[aceArt-GmbH]

See https://github.com/0x00000001A/es6-string-html with its /* sql */ syntax