RFR: 8358066: Non-ascii package names gives compilation error "import requires canonical name" [v2]

[Archie Cobbs]

> A simple counting bug in `Convert.utfNumChars()` causes bogus compiler errors for `import` statements of non-ASCII class names when the compiler is configured to use one of the older UTF-8 based `Name` table implementations (e.g., by specifying the `-XDuseUnsharedTable=true` flag).

Archie Cobbs has updated the pull request incrementally with two additional commits since the last revision:

 - Fix glitch in exception message.
 - Simplify code using review suggestion.

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25567/files
  - new: https://git.openjdk.org/jdk/pull/25567/files/18f9c0c9..4967cac9

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25567&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25567&range=00-01

  Stats: 7 lines in 2 files changed: 0 ins; 3 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/25567.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25567/head:pull/25567

PR: https://git.openjdk.org/jdk/pull/25567