RFR: JDK-8315921: Invalid CSS declarations in java.lang class documentation

[Hannes Wallnöfer]

This change fixes two errors in inline HTML styles in the `java.lang` package: 

 - wrong CSS property name in `java.lang.String` 
 - CSS declaration terminated by colon instead of semicolon in `java.lang.Thread`

Both errors caused the style declarations to be ignored and an error message to be shown in the browser console. 

The bug is `noreg-doc`, I tested the docs in the browser to make sure the error message is gone and the HTML displays as intended.

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Commit messages:
 - JDK-8315921: Invalid CSS declarations in java.lang class documentation

Changes: https://git.openjdk.org/jdk/pull/15762/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15762&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8315921
  Stats: 3 lines in 2 files changed: 0 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15762.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15762/head:pull/15762

PR: https://git.openjdk.org/jdk/pull/15762