RFR: 8267870: Remove unnecessary char_converter during class loading [v3]

[Coleen Phillimore]

> We create a String object from a Symbol, then swap the '/' for '.' characters, and create another String object.  Seems wasteful.  Removed java_lang_String::char_converted and made externalize_classname take a Symbol.
> 
> Tested with tier1-3 in mach5.

Coleen Phillimore has updated the pull request incrementally with one additional commit since the last revision:

  Fix CHECK_NULL.

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4173/files
  - new: https://git.openjdk.java.net/jdk/pull/4173/files/afbffd45..d4ec0270

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4173&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4173&range=01-02

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4173.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4173/head:pull/4173

PR: https://git.openjdk.java.net/jdk/pull/4173