RFR: 8075: Improve Eclipse development experience [v2]

[Christoph Langer]

> This PR merely updates the .classpath files to the state they would end up in when you do `Maven -> Update project ...` in current Eclipse.
> 
> There were only 2 manual changes:
> 1. I updated/corrected application/org.openjdk.jmc.flightrecorder.dependencyview/build.properties
> 2. I removed application/org.openjdk.jmc.browser.attach/.settings/org.eclipse.jdt.core.prefs because it gets generated upon Eclipse import anyway. Unfortunately it does not serve the use as a workaround for deselecting the `--release` compiler option.
> 
> In addition to that, I polished the devguide a little bit to hopefully make it more clear and stringent.

Christoph Langer has updated the pull request incrementally with one additional commit since the last revision:

  Fix typo

-------------

Changes:
  - all: https://git.openjdk.org/jmc/pull/489/files
  - new: https://git.openjdk.org/jmc/pull/489/files/c77959d7..c9a1f3d3

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jmc&pr=489&range=01
 - incr: https://webrevs.openjdk.org/?repo=jmc&pr=489&range=00-01

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/jmc/pull/489.diff
  Fetch: git fetch https://git.openjdk.org/jmc.git pull/489/head:pull/489

PR: https://git.openjdk.org/jmc/pull/489