RFR: 8285452: Add a new test library API to replace a file content using FileUtils.java [v7]

[Sibabrata Sahoo]

> A new API to support replacing selective lines with desired content.

Sibabrata Sahoo has updated the pull request incrementally with one additional commit since the last revision:

  8285452: updated to use lines()

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Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8360/files
  - new: https://git.openjdk.java.net/jdk/pull/8360/files/da6a214a..0b7dc2f9

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8360&range=06
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8360&range=05-06

  Stats: 2 lines in 1 file changed: 0 ins; 0 del; 2 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8360.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8360/head:pull/8360

PR: https://git.openjdk.java.net/jdk/pull/8360